diff --git a/src/include/mx/api/ApiCommon.h b/src/include/mx/api/ApiCommon.h
index 3ff4433aa..6efabd4b0 100644
--- a/src/include/mx/api/ApiCommon.h
+++ b/src/include/mx/api/ApiCommon.h
@@ -32,6 +32,17 @@ constexpr int NUMBER_LEVEL_UNSPECIFIED = -1; // MusicXML 'number' attributes, e.
 constexpr int VALUE_UNSPECIFIED = -1;        // other absent-able ints, e.g. DirectionData::voice
 constexpr Double DOUBLE_UNSPECIFIED = -1.0;  // absent-able doubles, e.g. StaffData::staffSize
 
+// MusicXML lets most elements carry an optional id attribute, a name that identifies that one
+// element within the document. Software uses it to point at a particular note, measure, or
+// marking -- to line playback up with the score, to hang an annotation on a note, or to link one
+// file to another. Every mx::api type that models such an element has an `id` member. Leave it
+// empty and no id attribute is written.
+//
+// An id must be unique within the document and must follow the XML name rules: a letter or an
+// underscore first, then letters, digits, dots, hyphens, or underscores. mx repairs an id that
+// breaks the name rules when it writes the file, but it does not check uniqueness, so an id you
+// invent must not collide with one already in the score.
+
 // Intentional ternary: absent-able bools use Bool::unspecified, not std::optional<bool>.
 // See "mx::api conventions" in AGENTS.md.
 enum class Bool
diff --git a/src/include/mx/api/BarlineData.h b/src/include/mx/api/BarlineData.h
index 967a5112b..05857f979 100644
--- a/src/include/mx/api/BarlineData.h
+++ b/src/include/mx/api/BarlineData.h
@@ -116,10 +116,13 @@ class BarlineData
     RepeatWinged repeatWinged;
     HorizontalAlignment location;
 
+    // The <barline> element's id attribute (see ApiCommon.h).
+    std::optional<std::string> id;
+
     BarlineData()
         : tickTimePosition{0}, barlineType{BarlineType::normal}, ending{}, repeat{false}, repeatTimes{0},
           repeatDirection{RepeatDirection::unspecified}, repeatAfterJump{Bool::unspecified},
-          repeatWinged{RepeatWinged::unspecified}, location{HorizontalAlignment::unspecified}
+          repeatWinged{RepeatWinged::unspecified}, location{HorizontalAlignment::unspecified}, id{}
     {
     }
 };
@@ -134,6 +137,7 @@ MXAPI_EQUALS_MEMBER(repeatDirection)
 MXAPI_EQUALS_MEMBER(repeatAfterJump)
 MXAPI_EQUALS_MEMBER(repeatWinged)
 MXAPI_EQUALS_MEMBER(location)
+MXAPI_EQUALS_MEMBER(id)
 MXAPI_EQUALS_END;
 MXAPI_NOT_EQUALS_AND_VECTORS(BarlineData);
 } // namespace api
diff --git a/src/include/mx/api/ClefData.h b/src/include/mx/api/ClefData.h
index c4feba6cd..81a788a87 100644
--- a/src/include/mx/api/ClefData.h
+++ b/src/include/mx/api/ClefData.h
@@ -6,6 +6,9 @@
 
 #include "mx/api/ApiCommon.h"
 
+#include <optional>
+#include <string>
+
 namespace mx
 {
 namespace api
@@ -67,6 +70,10 @@ class ClefData
     // Visibility of the clef via the MusicXML print-object attribute.
     // unspecified -> omit the attribute, yes/no -> write print-object verbatim.
     Bool printObject;
+
+    // The <clef> element's id attribute (see ApiCommon.h).
+    std::optional<std::string> id;
+
     std::string toString() const;
 
     // convenience - set symbol, line and octave for common clefs
@@ -99,6 +106,7 @@ MXAPI_EQUALS_MEMBER(tickTimePosition)
 MXAPI_EQUALS_MEMBER(location)
 MXAPI_EQUALS_MEMBER(additional)
 MXAPI_EQUALS_MEMBER(printObject)
+MXAPI_EQUALS_MEMBER(id)
 MXAPI_EQUALS_END;
 MXAPI_NOT_EQUALS_AND_VECTORS(ClefData);
 } // namespace api
diff --git a/src/include/mx/api/CurveData.h b/src/include/mx/api/CurveData.h
index 8b9670a9d..178919df6 100644
--- a/src/include/mx/api/CurveData.h
+++ b/src/include/mx/api/CurveData.h
@@ -10,6 +10,9 @@
 #include "mx/api/PositionData.h"
 #include "mx/api/SpannerNumber.h"
 
+#include <optional>
+#include <string>
+
 // MusicXML Documentation for Bezier Attributes Group
 // The bezier attribute group is used to indicate the curvature of slurs
 // and ties, representing the control points for a cubic bezier curve.
@@ -100,9 +103,13 @@ struct CurveStart
     bool isColorSpecified;
     ColorData colorData;
 
+    // The id attribute of the element this curve end is written as -- <slur> for a slur,
+    // <tied> for a tie (see ApiCommon.h).
+    std::optional<std::string> id;
+
     CurveStart(CurveType inCurveType)
         : curveType{inCurveType}, number{}, curvePoints{}, curveOrientation{CurveOrientation::unspecified},
-          placement{Placement::unspecified}, lineData{}, isColorSpecified{false}, colorData{}
+          placement{Placement::unspecified}, lineData{}, isColorSpecified{false}, colorData{}, id{}
     {
     }
 };
@@ -119,9 +126,13 @@ struct CurveContinue
     bool isBezierOffset2Specified;
     double bezierOffset2;
 
+    // The id attribute of the element this curve end is written as -- <slur> for a slur,
+    // <tied> for a tie (see ApiCommon.h).
+    std::optional<std::string> id;
+
     CurveContinue(CurveType inCurveType)
         : curveType{inCurveType}, number{}, curvePoints{}, isBezierX2Specified{false}, bezierX2{0.0},
-          isBezierY2Specified{false}, bezierY2{0.0}, isBezierOffset2Specified{false}, bezierOffset2{0.0}
+          isBezierY2Specified{false}, bezierY2{0.0}, isBezierOffset2Specified{false}, bezierOffset2{0.0}, id{}
     {
     }
 };
@@ -132,7 +143,11 @@ struct CurveStop
     SpannerNumber number;
     CurvePoints curvePoints;
 
-    CurveStop(CurveType inCurveType) : curveType{inCurveType}, number{}, curvePoints{}
+    // The id attribute of the element this curve end is written as -- <slur> for a slur,
+    // <tied> for a tie (see ApiCommon.h).
+    std::optional<std::string> id;
+
+    CurveStop(CurveType inCurveType) : curveType{inCurveType}, number{}, curvePoints{}, id{}
     {
     }
 };
@@ -157,6 +172,7 @@ MXAPI_EQUALS_MEMBER(placement)
 MXAPI_EQUALS_MEMBER(lineData)
 MXAPI_EQUALS_MEMBER(isColorSpecified)
 MXAPI_EQUALS_MEMBER(colorData)
+MXAPI_EQUALS_MEMBER(id)
 MXAPI_EQUALS_END;
 MXAPI_NOT_EQUALS_AND_VECTORS(CurveStart);
 
@@ -170,6 +186,7 @@ MXAPI_EQUALS_MEMBER(isBezierY2Specified)
 MXAPI_EQUALS_MEMBER(bezierY2)
 MXAPI_EQUALS_MEMBER(isBezierOffset2Specified)
 MXAPI_EQUALS_MEMBER(bezierOffset2)
+MXAPI_EQUALS_MEMBER(id)
 MXAPI_EQUALS_END;
 MXAPI_NOT_EQUALS_AND_VECTORS(CurveContinue);
 
@@ -177,6 +194,7 @@ MXAPI_EQUALS_BEGIN(CurveStop)
 MXAPI_EQUALS_MEMBER(curveType)
 MXAPI_EQUALS_MEMBER(number)
 MXAPI_EQUALS_MEMBER(curvePoints)
+MXAPI_EQUALS_MEMBER(id)
 MXAPI_EQUALS_END;
 MXAPI_NOT_EQUALS_AND_VECTORS(CurveStop);
 } // namespace api
diff --git a/src/include/mx/api/DirectionData.h b/src/include/mx/api/DirectionData.h
index a4f61fae6..6981d2200 100644
--- a/src/include/mx/api/DirectionData.h
+++ b/src/include/mx/api/DirectionData.h
@@ -11,6 +11,7 @@
 #include "mx/api/SoundData.h"
 
 #include <optional>
+#include <string>
 
 namespace mx
 {
@@ -80,10 +81,13 @@ struct DirectionData
     // serialize as their own <figured-bass> elements, not as direction-type content.
     std::vector<FiguredBassData> figuredBasses;
 
+    // The <direction> element's id attribute (see ApiCommon.h).
+    std::optional<std::string> id;
+
     DirectionData()
         : tickTimePosition{0}, placement{Placement::unspecified}, systemRelation{SystemRelation::unspecified}, offset{},
           voice{VALUE_UNSPECIFIED}, isStaffValueSpecified{true}, isSoundDataSpecified{false}, soundData{},
-          directionTypes{}, chords{}, figuredBasses{}
+          directionTypes{}, chords{}, figuredBasses{}, id{}
     {
     }
 };
@@ -106,6 +110,7 @@ MXAPI_EQUALS_MEMBER(soundData)
 MXAPI_EQUALS_MEMBER(directionTypes)
 MXAPI_EQUALS_MEMBER(chords)
 MXAPI_EQUALS_MEMBER(figuredBasses)
+MXAPI_EQUALS_MEMBER(id)
 MXAPI_EQUALS_END;
 MXAPI_NOT_EQUALS_AND_VECTORS(DirectionData);
 } // namespace api
diff --git a/src/include/mx/api/FiguredBassData.h b/src/include/mx/api/FiguredBassData.h
index 26263fbdd..a4ff4d9eb 100644
--- a/src/include/mx/api/FiguredBassData.h
+++ b/src/include/mx/api/FiguredBassData.h
@@ -6,6 +6,7 @@
 
 #include "mx/api/ApiCommon.h"
 
+#include <optional>
 #include <string>
 #include <vector>
 
@@ -48,7 +49,10 @@ class FiguredBassData
     // The optional <duration>, in ticks. A value less than 0 means 'unspecified' (no duration child).
     int durationTimeTicks;
 
-    FiguredBassData() : figures{}, parentheses{Bool::unspecified}, durationTimeTicks{VALUE_UNSPECIFIED}
+    // The <figured-bass> element's id attribute (see ApiCommon.h).
+    std::optional<std::string> id;
+
+    FiguredBassData() : figures{}, parentheses{Bool::unspecified}, durationTimeTicks{VALUE_UNSPECIFIED}, id{}
     {
     }
 };
@@ -57,6 +61,7 @@ MXAPI_EQUALS_BEGIN(FiguredBassData)
 MXAPI_EQUALS_MEMBER(figures)
 MXAPI_EQUALS_MEMBER(parentheses)
 MXAPI_EQUALS_MEMBER(durationTimeTicks)
+MXAPI_EQUALS_MEMBER(id)
 MXAPI_EQUALS_END;
 MXAPI_NOT_EQUALS_AND_VECTORS(FiguredBassData);
 
diff --git a/src/include/mx/api/KeyData.h b/src/include/mx/api/KeyData.h
index f4551b371..ff4666ae0 100644
--- a/src/include/mx/api/KeyData.h
+++ b/src/include/mx/api/KeyData.h
@@ -6,6 +6,9 @@
 #include "mx/api/ApiCommon.h"
 #include "mx/api/KeyComponent.h"
 
+#include <optional>
+#include <string>
+
 namespace mx
 {
 namespace api
@@ -121,9 +124,12 @@ struct KeyData
     // alterations. When custom is non-empty, then fifths and mode are ignored.
     std::vector<KeyComponent> nonTraditional;
 
+    // The <key> element's id attribute (see ApiCommon.h).
+    std::optional<std::string> id;
+
     KeyData()
         : fifths{0}, cancel{0}, cancelLocation{CancelLocation::unspecified}, mode{KeyMode::unspecified},
-          tickTimePosition{0}, staffIndex{INDEX_UNSPECIFIED}, nonTraditional{}
+          tickTimePosition{0}, staffIndex{INDEX_UNSPECIFIED}, nonTraditional{}, id{}
     {
     }
 };
@@ -136,6 +142,7 @@ MXAPI_EQUALS_MEMBER(mode)
 MXAPI_EQUALS_MEMBER(tickTimePosition)
 MXAPI_EQUALS_MEMBER(staffIndex)
 MXAPI_EQUALS_MEMBER(nonTraditional)
+MXAPI_EQUALS_MEMBER(id)
 MXAPI_EQUALS_END;
 
 MXAPI_NOT_EQUALS_AND_VECTORS(KeyData);
diff --git a/src/include/mx/api/LyricData.h b/src/include/mx/api/LyricData.h
index f88c6f216..e08993b94 100644
--- a/src/include/mx/api/LyricData.h
+++ b/src/include/mx/api/LyricData.h
@@ -8,6 +8,9 @@
 #include "mx/api/PositionData.h"
 #include "mx/api/PrintData.h"
 
+#include <optional>
+#include <string>
+
 namespace mx
 {
 namespace api
@@ -38,7 +41,7 @@ class LyricData
   public:
     LyricData()
         : text{}, verseNumber{}, verseName{}, syllabic{LyricSyllabic::unspecified}, hasExtend{false},
-          extendType{LyricExtendType::unspecified}, positionData{}, printData{}
+          extendType{LyricExtendType::unspecified}, positionData{}, printData{}, id{}
     {
     }
 
@@ -50,6 +53,9 @@ class LyricData
     LyricExtendType extendType;
     PositionData positionData;
     PrintData printData;
+
+    // The <lyric> element's id attribute (see ApiCommon.h).
+    std::optional<std::string> id;
 };
 
 MXAPI_EQUALS_BEGIN(LyricData)
@@ -61,6 +67,7 @@ MXAPI_EQUALS_MEMBER(hasExtend)
 MXAPI_EQUALS_MEMBER(extendType)
 MXAPI_EQUALS_MEMBER(positionData)
 MXAPI_EQUALS_MEMBER(printData)
+MXAPI_EQUALS_MEMBER(id)
 MXAPI_EQUALS_END;
 MXAPI_NOT_EQUALS_AND_VECTORS(LyricData);
 } // namespace api
diff --git a/src/include/mx/api/MeasureData.h b/src/include/mx/api/MeasureData.h
index 8a6cde682..6968b6daa 100644
--- a/src/include/mx/api/MeasureData.h
+++ b/src/include/mx/api/MeasureData.h
@@ -111,6 +111,9 @@ class MeasureData
     // before this field existed.
     std::vector<TransposeData> transpositions;
 
+    // The <measure> element's id attribute (see ApiCommon.h).
+    std::optional<std::string> id;
+
     MeasureData()
         : staves{}, timeSignature{}, number{}, measureNumbering{MeasureNumbering::unspecified},
           measureNumberingMultipleRestAlways{Bool::unspecified}, measureNumberingMultipleRestRange{Bool::unspecified},
@@ -141,6 +144,7 @@ MXAPI_EQUALS_MEMBER(keys)
 MXAPI_EQUALS_MEMBER(barlines)
 MXAPI_EQUALS_MEMBER(partSymbol)
 MXAPI_EQUALS_MEMBER(transpositions)
+MXAPI_EQUALS_MEMBER(id)
 MXAPI_EQUALS_END;
 MXAPI_NOT_EQUALS_AND_VECTORS(MeasureData);
 } // namespace api
diff --git a/src/include/mx/api/NoteData.h b/src/include/mx/api/NoteData.h
index 79129b482..d746d18b7 100644
--- a/src/include/mx/api/NoteData.h
+++ b/src/include/mx/api/NoteData.h
@@ -82,7 +82,11 @@ struct TieLetRing
     bool isColorSpecified;
     ColorData colorData;
 
-    TieLetRing() : positionData{}, curveOrientation{CurveOrientation::unspecified}, isColorSpecified{false}, colorData{}
+    // The <tied> element's id attribute (see ApiCommon.h).
+    std::optional<std::string> id;
+
+    TieLetRing()
+        : positionData{}, curveOrientation{CurveOrientation::unspecified}, isColorSpecified{false}, colorData{}, id{}
     {
     }
 };
@@ -92,6 +96,7 @@ MXAPI_EQUALS_MEMBER(positionData)
 MXAPI_EQUALS_MEMBER(curveOrientation)
 MXAPI_EQUALS_MEMBER(isColorSpecified)
 MXAPI_EQUALS_MEMBER(colorData)
+MXAPI_EQUALS_MEMBER(id)
 MXAPI_EQUALS_END;
 MXAPI_NOT_EQUALS_AND_VECTORS(TieLetRing);
 
@@ -202,6 +207,9 @@ class NoteData
     // similarly when parsing if we see ##misc-data## in this element, it
     // will be parsed into these strings. do not use commas in your misc
     // data strings as these are the delimiter
+
+    // The <note> element's id attribute (see ApiCommon.h).
+    std::optional<std::string> id;
     std::vector<std::string> miscData;
 };
 
@@ -234,6 +242,7 @@ MXAPI_EQUALS_MEMBER(printData)
 MXAPI_EQUALS_MEMBER(noteAttachmentData)
 MXAPI_EQUALS_MEMBER(lyrics)
 MXAPI_EQUALS_MEMBER(miscData)
+MXAPI_EQUALS_MEMBER(id)
 MXAPI_EQUALS_END;
 MXAPI_NOT_EQUALS_AND_VECTORS(NoteData);
 } // namespace api
diff --git a/src/include/mx/api/PedalLineData.h b/src/include/mx/api/PedalLineData.h
index 53c5c6c64..8606bcfc9 100644
--- a/src/include/mx/api/PedalLineData.h
+++ b/src/include/mx/api/PedalLineData.h
@@ -7,6 +7,9 @@
 #include "mx/api/ApiCommon.h"
 #include "mx/api/PositionData.h"
 
+#include <optional>
+#include <string>
+
 namespace mx
 {
 namespace api
@@ -50,11 +53,14 @@ struct PedalLineData
     int tickTimePosition;
     PositionData positionData;
 
-    PedalLineData() : kind{PedalLineKind::unspecified}, tickTimePosition{0}, positionData{}
+    // The <pedal> element's id attribute (see ApiCommon.h).
+    std::optional<std::string> id;
+
+    PedalLineData() : kind{PedalLineKind::unspecified}, tickTimePosition{0}, positionData{}, id{}
     {
     }
 
-    PedalLineData(PedalLineKind inKind) : kind{inKind}, tickTimePosition{0}, positionData{}
+    PedalLineData(PedalLineKind inKind) : kind{inKind}, tickTimePosition{0}, positionData{}, id{}
     {
     }
 };
@@ -63,6 +69,7 @@ MXAPI_EQUALS_BEGIN(PedalLineData)
 MXAPI_EQUALS_MEMBER(kind)
 MXAPI_EQUALS_MEMBER(tickTimePosition)
 MXAPI_EQUALS_MEMBER(positionData)
+MXAPI_EQUALS_MEMBER(id)
 MXAPI_EQUALS_END;
 MXAPI_NOT_EQUALS_AND_VECTORS(PedalLineData);
 } // namespace api
diff --git a/src/include/mx/api/RehearsalData.h b/src/include/mx/api/RehearsalData.h
index 73685bcfd..a34430155 100644
--- a/src/include/mx/api/RehearsalData.h
+++ b/src/include/mx/api/RehearsalData.h
@@ -9,6 +9,9 @@
 #include "mx/api/FontData.h"
 #include "mx/api/PositionData.h"
 
+#include <optional>
+#include <string>
+
 namespace mx
 {
 namespace api
@@ -32,9 +35,12 @@ class RehearsalData
     // and says which edge of the text the position refers to; MusicXML defines both.
     HorizontalAlignment justify;
 
+    // The <rehearsal> element's id attribute (see ApiCommon.h).
+    std::optional<std::string> id;
+
     RehearsalData()
         : text{}, positionData{}, isColorSpecified{false}, colorData{}, fontData{}, enclosure{Enclosure::unspecified},
-          justify{HorizontalAlignment::unspecified}
+          justify{HorizontalAlignment::unspecified}, id{}
     {
     }
 };
@@ -47,6 +53,7 @@ MXAPI_EQUALS_MEMBER(colorData)
 MXAPI_EQUALS_MEMBER(fontData)
 MXAPI_EQUALS_MEMBER(enclosure)
 MXAPI_EQUALS_MEMBER(justify)
+MXAPI_EQUALS_MEMBER(id)
 MXAPI_EQUALS_END;
 MXAPI_NOT_EQUALS_AND_VECTORS(RehearsalData);
 } // namespace api
diff --git a/src/include/mx/api/SoundData.h b/src/include/mx/api/SoundData.h
index 010080e37..121a12999 100644
--- a/src/include/mx/api/SoundData.h
+++ b/src/include/mx/api/SoundData.h
@@ -87,10 +87,13 @@ struct SoundData
 
     std::optional<SwingData> swing;
 
+    // The <sound> element's id attribute (see ApiCommon.h).
+    std::optional<std::string> id;
+
     SoundData()
         : tempo{DOUBLE_UNSPECIFIED}, dynamics{DOUBLE_UNSPECIFIED}, dacapo{Bool::unspecified},
           forwardRepeat{Bool::unspecified}, pizzicato{Bool::unspecified}, segno{}, dalsegno{}, coda{}, tocoda{}, fine{},
-          swing{}
+          swing{}, id{}
     {
     }
 
@@ -98,7 +101,7 @@ struct SoundData
     {
         return tempo >= 0.0 || dynamics >= 0.0 || dacapo != Bool::unspecified || forwardRepeat != Bool::unspecified ||
                pizzicato != Bool::unspecified || !segno.empty() || !dalsegno.empty() || !coda.empty() ||
-               !tocoda.empty() || !fine.empty() || swing.has_value();
+               !tocoda.empty() || !fine.empty() || swing.has_value() || id.has_value();
     }
 };
 
@@ -123,6 +126,7 @@ MXAPI_EQUALS_MEMBER(coda)
 MXAPI_EQUALS_MEMBER(tocoda)
 MXAPI_EQUALS_MEMBER(fine)
 MXAPI_EQUALS_MEMBER(swing)
+MXAPI_EQUALS_MEMBER(id)
 MXAPI_EQUALS_END;
 MXAPI_NOT_EQUALS_AND_VECTORS(SoundData);
 } // namespace api
diff --git a/src/include/mx/api/SpannerData.h b/src/include/mx/api/SpannerData.h
index 51645990f..dd7c55d8a 100644
--- a/src/include/mx/api/SpannerData.h
+++ b/src/include/mx/api/SpannerData.h
@@ -10,6 +10,7 @@
 #include "mx/api/PrintData.h"
 #include "mx/api/SpannerNumber.h"
 
+#include <optional>
 #include <string>
 
 namespace mx
@@ -25,7 +26,11 @@ struct SpannerStart
     PrintData printData;
     LineData lineData;
 
-    SpannerStart() : number{}, tickTimePosition{0}, positionData{}, printData{}, lineData{}
+    // The id attribute of the element this spanner end is written as -- <bracket>,
+    // <dashes>, or <octave-shift> (see ApiCommon.h).
+    std::optional<std::string> id;
+
+    SpannerStart() : number{}, tickTimePosition{0}, positionData{}, printData{}, lineData{}, id{}
     {
     }
 };
@@ -37,7 +42,11 @@ struct SpannerStop
     PositionData positionData;
     LineData lineData;
 
-    SpannerStop() : number{}, tickTimePosition{0}, positionData{}, lineData{}
+    // The id attribute of the element this spanner end is written as -- <bracket>,
+    // <dashes>, or <octave-shift> (see ApiCommon.h).
+    std::optional<std::string> id;
+
+    SpannerStop() : number{}, tickTimePosition{0}, positionData{}, lineData{}, id{}
     {
     }
 };
@@ -48,6 +57,7 @@ MXAPI_EQUALS_MEMBER(tickTimePosition)
 MXAPI_EQUALS_MEMBER(positionData)
 MXAPI_EQUALS_MEMBER(printData)
 MXAPI_EQUALS_MEMBER(lineData)
+MXAPI_EQUALS_MEMBER(id)
 MXAPI_EQUALS_END;
 MXAPI_NOT_EQUALS_AND_VECTORS(SpannerStart);
 
@@ -56,6 +66,7 @@ MXAPI_EQUALS_MEMBER(number)
 MXAPI_EQUALS_MEMBER(tickTimePosition)
 MXAPI_EQUALS_MEMBER(positionData)
 MXAPI_EQUALS_MEMBER(lineData)
+MXAPI_EQUALS_MEMBER(id)
 MXAPI_EQUALS_END;
 MXAPI_NOT_EQUALS_AND_VECTORS(SpannerStop);
 } // namespace api
diff --git a/src/include/mx/api/SymbolData.h b/src/include/mx/api/SymbolData.h
index 8b6d88742..3b215534b 100644
--- a/src/include/mx/api/SymbolData.h
+++ b/src/include/mx/api/SymbolData.h
@@ -41,9 +41,12 @@ class SymbolData
     // symbol-formatting attributes mirror the text-formatting ones on `<words>`.
     HorizontalAlignment justify;
 
+    // The <symbol> element's id attribute (see ApiCommon.h).
+    std::optional<std::string> id;
+
     SymbolData()
         : smufl{}, positionData{}, fontData{}, color{}, enclosure{Enclosure::unspecified},
-          justify{HorizontalAlignment::unspecified}
+          justify{HorizontalAlignment::unspecified}, id{}
     {
     }
 };
@@ -55,6 +58,7 @@ MXAPI_EQUALS_MEMBER(fontData)
 MXAPI_EQUALS_MEMBER(color)
 MXAPI_EQUALS_MEMBER(enclosure)
 MXAPI_EQUALS_MEMBER(justify)
+MXAPI_EQUALS_MEMBER(id)
 MXAPI_EQUALS_END;
 MXAPI_NOT_EQUALS_AND_VECTORS(SymbolData);
 } // namespace api
diff --git a/src/include/mx/api/TimeChoice.h b/src/include/mx/api/TimeChoice.h
index a16a3fcb1..d26ba44e2 100644
--- a/src/include/mx/api/TimeChoice.h
+++ b/src/include/mx/api/TimeChoice.h
@@ -8,6 +8,8 @@
 #include "mx/api/ComplexTimeSignature.h"
 #include "mx/api/TimeSignatureData.h"
 
+#include <optional>
+#include <string>
 #include <variant>
 
 namespace mx
@@ -57,6 +59,10 @@ class TimeChoice
     // Print/hide the time signature (<time print-object=...>). Ignored when isImplicit.
     Bool display{Bool::unspecified};
 
+    // The <time> element's id attribute (see ApiCommon.h). Only the measure that states the time
+    // signature carries it; a measure that inherits the signature (isImplicit) has no id.
+    std::optional<std::string> id;
+
     // Defaults to a simple, implicit 4/4.
     TimeChoice();
 
diff --git a/src/include/mx/api/TransposeData.h b/src/include/mx/api/TransposeData.h
index d5c55a99b..ac678af64 100644
--- a/src/include/mx/api/TransposeData.h
+++ b/src/include/mx/api/TransposeData.h
@@ -6,6 +6,9 @@
 
 #include "mx/api/ApiCommon.h"
 
+#include <optional>
+#include <string>
+
 namespace mx
 {
 namespace api
@@ -70,6 +73,9 @@ class TransposeData
     /// Supports a transposition change somewhere other than at the start of a measure.
     int tickTimePosition = 0;
 
+    /// The <transpose> element's id attribute (see ApiCommon.h).
+    std::optional<std::string> id;
+
     /// If both chromatic and diatonic are zero, then TransposeData is unused (i.e. it need
     /// not be encoded in the MusicXML output).
     inline bool isUsed() const
@@ -83,6 +89,7 @@ MXAPI_EQUALS_MEMBER(chromatic)
 MXAPI_EQUALS_MEMBER(diatonic)
 MXAPI_EQUALS_MEMBER(staffIndex)
 MXAPI_EQUALS_MEMBER(tickTimePosition)
+MXAPI_EQUALS_MEMBER(id)
 MXAPI_EQUALS_END;
 MXAPI_NOT_EQUALS_AND_VECTORS(TransposeData);
 } // namespace api
diff --git a/src/include/mx/api/TupletData.h b/src/include/mx/api/TupletData.h
index 3991f1106..7868c564f 100644
--- a/src/include/mx/api/TupletData.h
+++ b/src/include/mx/api/TupletData.h
@@ -9,6 +9,9 @@
 #include "mx/api/LineData.h"
 #include "mx/api/PositionData.h"
 
+#include <optional>
+#include <string>
+
 namespace mx
 {
 namespace api
@@ -46,12 +49,15 @@ class TupletStart
 
     Bool bracket;
 
+    // The <tuplet> element's id attribute (see ApiCommon.h).
+    std::optional<std::string> id;
+
     TupletStart()
         : numberLevel{NUMBER_LEVEL_UNSPECIFIED}, positionData{}, actualNumber{VALUE_UNSPECIFIED},
           actualDurationName{api::DurationName::unspecified}, actualDots{VALUE_UNSPECIFIED},
           normalNumber{VALUE_UNSPECIFIED}, normalDurationName{api::DurationName::unspecified},
           normalDots{VALUE_UNSPECIFIED}, showActualNumber{Bool::unspecified}, showNormalNumber{Bool::unspecified},
-          bracket{Bool::unspecified}
+          bracket{Bool::unspecified}, id{}
     {
     }
 };
@@ -65,7 +71,10 @@ class TupletStop
 
     PositionData positionData;
 
-    TupletStop() : numberLevel{NUMBER_LEVEL_UNSPECIFIED}, positionData{}
+    // The <tuplet> element's id attribute (see ApiCommon.h).
+    std::optional<std::string> id;
+
+    TupletStop() : numberLevel{NUMBER_LEVEL_UNSPECIFIED}, positionData{}, id{}
     {
     }
 };
@@ -82,12 +91,14 @@ MXAPI_EQUALS_MEMBER(normalDots)
 MXAPI_EQUALS_MEMBER(showActualNumber)
 MXAPI_EQUALS_MEMBER(showNormalNumber)
 MXAPI_EQUALS_MEMBER(bracket)
+MXAPI_EQUALS_MEMBER(id)
 MXAPI_EQUALS_END;
 MXAPI_NOT_EQUALS_AND_VECTORS(TupletStart);
 
 MXAPI_EQUALS_BEGIN(TupletStop)
 MXAPI_EQUALS_MEMBER(numberLevel)
 MXAPI_EQUALS_MEMBER(positionData)
+MXAPI_EQUALS_MEMBER(id)
 MXAPI_EQUALS_END;
 MXAPI_NOT_EQUALS_AND_VECTORS(TupletStop);
 } // namespace api
diff --git a/src/include/mx/api/WedgeData.h b/src/include/mx/api/WedgeData.h
index a307e0f6f..505a465d8 100644
--- a/src/include/mx/api/WedgeData.h
+++ b/src/include/mx/api/WedgeData.h
@@ -10,6 +10,9 @@
 #include "mx/api/PositionData.h"
 #include "mx/api/SpannerNumber.h"
 
+#include <optional>
+#include <string>
+
 namespace mx
 {
 namespace api
@@ -32,9 +35,12 @@ struct WedgeStart
     bool isColorSpecified;
     ColorData colorData;
 
+    // The <wedge> element's id attribute (see ApiCommon.h).
+    std::optional<std::string> id;
+
     WedgeStart()
         : number{}, wedgeType{WedgeType::unspecified}, isSpreadSpecified{false}, spread{0.0}, lineData{},
-          positionData{}, isColorSpecified{false}, colorData{}
+          positionData{}, isColorSpecified{false}, colorData{}, id{}
     {
     }
 };
@@ -46,7 +52,10 @@ struct WedgeStop
     bool isSpreadSpecified;
     double spread;
 
-    WedgeStop() : number{}, positionData{}, isSpreadSpecified{false}, spread{0.0}
+    // The <wedge> element's id attribute (see ApiCommon.h).
+    std::optional<std::string> id;
+
+    WedgeStop() : number{}, positionData{}, isSpreadSpecified{false}, spread{0.0}, id{}
     {
     }
 };
@@ -60,6 +69,7 @@ MXAPI_EQUALS_MEMBER(lineData)
 MXAPI_EQUALS_MEMBER(positionData)
 MXAPI_EQUALS_MEMBER(isColorSpecified)
 MXAPI_EQUALS_MEMBER(colorData)
+MXAPI_EQUALS_MEMBER(id)
 MXAPI_EQUALS_END;
 MXAPI_NOT_EQUALS_AND_VECTORS(WedgeStart);
 
@@ -68,6 +78,7 @@ MXAPI_EQUALS_MEMBER(number)
 MXAPI_EQUALS_MEMBER(positionData)
 MXAPI_EQUALS_MEMBER(isSpreadSpecified)
 MXAPI_EQUALS_MEMBER(spread)
+MXAPI_EQUALS_MEMBER(id)
 MXAPI_EQUALS_END;
 MXAPI_NOT_EQUALS_AND_VECTORS(WedgeStop);
 } // namespace api
diff --git a/src/include/mx/api/WordsData.h b/src/include/mx/api/WordsData.h
index 80e558f38..11fb1a096 100644
--- a/src/include/mx/api/WordsData.h
+++ b/src/include/mx/api/WordsData.h
@@ -9,6 +9,9 @@
 #include "mx/api/FontData.h"
 #include "mx/api/PositionData.h"
 
+#include <optional>
+#include <string>
+
 namespace mx
 {
 namespace api
@@ -35,9 +38,12 @@ class WordsData
     // block against its anchor point; MusicXML defines both attributes on `<words>`.
     HorizontalAlignment justify;
 
+    // The <words> element's id attribute (see ApiCommon.h).
+    std::optional<std::string> id;
+
     WordsData()
         : text{}, positionData{}, fontData{}, isColorSpecified{false}, colorData{}, enclosure{Enclosure::unspecified},
-          justify{HorizontalAlignment::unspecified}
+          justify{HorizontalAlignment::unspecified}, id{}
     {
     }
 };
@@ -50,6 +56,7 @@ MXAPI_EQUALS_MEMBER(isColorSpecified)
 MXAPI_EQUALS_MEMBER(colorData)
 MXAPI_EQUALS_MEMBER(enclosure)
 MXAPI_EQUALS_MEMBER(justify)
+MXAPI_EQUALS_MEMBER(id)
 MXAPI_EQUALS_END;
 MXAPI_NOT_EQUALS_AND_VECTORS(WordsData);
 } // namespace api
diff --git a/src/private/mx/api/TimeChoice.cpp b/src/private/mx/api/TimeChoice.cpp
index 789e012e3..ac4c2491f 100644
--- a/src/private/mx/api/TimeChoice.cpp
+++ b/src/private/mx/api/TimeChoice.cpp
@@ -111,7 +111,7 @@ const ComplexTimeSignature TimeChoice::complex() const
 
 bool TimeChoice::operator==(const TimeChoice &other) const
 {
-    return isImplicit == other.isImplicit && display == other.display && myValue == other.myValue;
+    return isImplicit == other.isImplicit && display == other.display && id == other.id && myValue == other.myValue;
 }
 
 } // namespace api
diff --git a/src/private/mx/impl/Converter.cpp b/src/private/mx/impl/Converter.cpp
index 8dc0b8709..f6e847fb4 100644
--- a/src/private/mx/impl/Converter.cpp
+++ b/src/private/mx/impl/Converter.cpp
@@ -6,6 +6,7 @@
 #include "mx/core/Decimal.h"
 #include "mx/core/generated/Semitones.h"
 #include "mx/core/generated/TransposeGroup.h"
+#include "mx/impl/IdFunctions.h"
 
 #include <algorithm>
 #include <cmath>
@@ -2323,7 +2324,9 @@ mx::api::TransposeData Converter::convertToTransposeData(const mx::core::Transpo
     const auto octaves = specifiedOctave.has_value() ? specifiedOctave.value() : 0;
     diatonic += octaves * 7;
     const auto chromatic = specifiedChromatic + (octaves * 12);
-    return mx::api::TransposeData{chromatic, diatonic};
+    mx::api::TransposeData out{chromatic, diatonic};
+    out.id = getId(inTranspose);
+    return out;
 }
 } // namespace impl
 } // namespace mx
diff --git a/src/private/mx/impl/CurveFunctions.h b/src/private/mx/impl/CurveFunctions.h
index 46992d7dc..26891aeda 100644
--- a/src/private/mx/impl/CurveFunctions.h
+++ b/src/private/mx/impl/CurveFunctions.h
@@ -8,6 +8,7 @@
 #include "mx/api/NoteData.h"
 #include "mx/core/generated/Slur.h"
 #include "mx/core/generated/Tied.h"
+#include "mx/impl/IdFunctions.h"
 #include "mx/impl/LineFunctions.h"
 #include "mx/impl/PositionFunctions.h"
 #include "mx/impl/PrintFunctions.h"
@@ -105,6 +106,8 @@ api::CurveStart parseCurveStart(const SLUR_OR_TIE_ELEMENT_TYPE &inSlurOrTie)
         c.curveOrientation = *inAttributes.orientation() == core::OverUnder::over() ? api::CurveOrientation::overhand
                                                                                     : api::CurveOrientation::underhand;
     }
+
+    c.id = getId(inAttributes);
     return c;
 }
 
@@ -139,6 +142,7 @@ api::CurveContinue parseCurveContinue(const SLUR_OR_TIE_ELEMENT_TYPE &inSlurOrTi
     }
 
     c.curvePoints = parseCurvePoints(inAttributes);
+    c.id = getId(inAttributes);
     return c;
 }
 
@@ -154,6 +158,7 @@ template <typename SLUR_OR_TIE_ELEMENT_TYPE> api::CurveStop parseCurveStop(const
     }
 
     c.curvePoints = parseCurvePoints(inAttributes);
+    c.id = getId(inAttributes);
     return c;
 }
 
@@ -167,6 +172,7 @@ void writeAttributesFromCurveStart(const api::CurveStart inCurve, ATTRIBUTES_TYP
 {
     using CurveTypeAttribute = std::decay_t<decltype(outAttributes.type())>;
     outAttributes.setType(CurveTypeAttribute::start());
+    impl::setId(inCurve.id, outAttributes);
     impl::setAttributesFromPositionData(inCurve.curvePoints.positionData, outAttributes);
     impl::setAttributesFromLineData(inCurve.lineData, outAttributes);
 
@@ -210,6 +216,7 @@ void writeAttributesFromCurveContinue(const api::CurveContinue inCurve, ATTRIBUT
 {
     using CurveTypeAttribute = std::decay_t<decltype(outAttributes.type())>;
     outAttributes.setType(CurveTypeAttribute::continue_());
+    impl::setId(inCurve.id, outAttributes);
     impl::setAttributesFromPositionData(inCurve.curvePoints.positionData, outAttributes);
 
     if (inResolvedNumber.has_value())
@@ -255,6 +262,7 @@ void writeAttributesFromCurveStop(const api::CurveStop inCurve, ATTRIBUTES_TYPE
 {
     using CurveTypeAttribute = std::decay_t<decltype(outAttributes.type())>;
     outAttributes.setType(CurveTypeAttribute::stop());
+    impl::setId(inCurve.id, outAttributes);
     impl::setAttributesFromPositionData(inCurve.curvePoints.positionData, outAttributes);
 
     if (inResolvedNumber.has_value())
@@ -285,6 +293,7 @@ inline void writeAttributesFromTieLetRing(const api::TieLetRing &inTie, core::Ti
 {
     outTied.setType(core::TiedType::letRing());
     impl::setAttributesFromPositionData(inTie.positionData, outTied);
+    impl::setId(inTie.id, outTied);
 
     if (inTie.isColorSpecified)
     {
@@ -318,6 +327,8 @@ inline api::TieLetRing parseTieLetRing(const core::Tied &inTied)
         c.curveOrientation = *inTied.orientation() == core::OverUnder::over() ? api::CurveOrientation::overhand
                                                                               : api::CurveOrientation::underhand;
     }
+
+    c.id = getId(inTied);
     return c;
 }
 
diff --git a/src/private/mx/impl/DirectionReader.cpp b/src/private/mx/impl/DirectionReader.cpp
index 8399af94c..b24135e33 100644
--- a/src/private/mx/impl/DirectionReader.cpp
+++ b/src/private/mx/impl/DirectionReader.cpp
@@ -84,6 +84,7 @@
 #include "mx/core/generated/WedgeType.h"
 #include "mx/core/generated/YesNo.h"
 #include "mx/impl/DynamicsReader.h"
+#include "mx/impl/IdFunctions.h"
 #include "mx/impl/MarkDataFunctions.h"
 #include "mx/impl/MetronomeReader.h"
 #include "mx/impl/PrintFunctions.h"
@@ -125,6 +126,7 @@ mx::api::DirectionData DirectionReader::initializeData()
     if (myDirection)
     {
         result.isStaffValueSpecified = myDirection->staff().has_value();
+        result.id = getId(*myDirection);
     }
     else if (myHarmony)
     {
@@ -367,6 +369,7 @@ void DirectionReader::parseRehearsal(const core::DirectionType &directionType)
         {
             outRehearsal.justify = myConverter.convert(*rehearsal.justify());
         }
+        outRehearsal.id = getId(rehearsal);
         myOutDirectionData.directionTypes.emplace_back(api::DirectionChoice{std::move(outRehearsal)});
     }
 }
@@ -428,6 +431,7 @@ void DirectionReader::parseWordsRun(const core::DirectionType &directionType)
             {
                 outSymbol.justify = myConverter.convert(*symbolEl.justify());
             }
+            outSymbol.id = getId(symbolEl);
             run.emplace_back(std::move(outSymbol));
             continue;
         }
@@ -449,6 +453,7 @@ void DirectionReader::parseWordsRun(const core::DirectionType &directionType)
         {
             outWords.justify = myConverter.convert(*wordEl.justify());
         }
+        outWords.id = getId(wordEl);
         run.emplace_back(std::move(outWords));
     }
 
@@ -510,6 +515,7 @@ void DirectionReader::parseWedge(const core::DirectionType &directionType)
             stop.spread = spread;
         }
         stop.positionData = positionData;
+        stop.id = getId(wedge);
         myOutDirectionData.directionTypes.emplace_back(api::DirectionChoice{std::move(stop)});
         return;
     }
@@ -530,6 +536,7 @@ void DirectionReader::parseWedge(const core::DirectionType &directionType)
         start.lineData = lineData;
         start.isColorSpecified = isColorSpecified;
         start.colorData = colorData;
+        start.id = getId(wedge);
         myOutDirectionData.directionTypes.emplace_back(api::DirectionChoice{std::move(start)});
     }
 }
@@ -622,6 +629,7 @@ void DirectionReader::parseBracket(const core::DirectionType &directionType)
         start.positionData = this->parsePositionData(bracket);
         start.lineData = makeBracketLineData();
         start.printData = impl::getPrintData(bracket);
+        start.id = getId(bracket);
         myOutDirectionData.directionTypes.emplace_back(api::DirectionChoice::bracketStart(std::move(start)));
         return;
     }
@@ -677,6 +685,7 @@ void DirectionReader::parsePedal(const core::DirectionType &directionType)
         pedalData.tickTimePosition = myOutDirectionData.tickTimePosition;
         pedalData.positionData = getPositionData(pedal);
         pedalData.positionData.placement = placement;
+        pedalData.id = getId(pedal);
         myOutDirectionData.directionTypes.emplace_back(api::DirectionChoice{std::move(pedalData)});
         return;
     }
diff --git a/src/private/mx/impl/DirectionWriter.cpp b/src/private/mx/impl/DirectionWriter.cpp
index a861a3bec..dfeb9fefb 100644
--- a/src/private/mx/impl/DirectionWriter.cpp
+++ b/src/private/mx/impl/DirectionWriter.cpp
@@ -109,6 +109,7 @@
 #include "mx/core/generated/YesNo.h"
 #include "mx/impl/DynamicsWriter.h"
 #include "mx/impl/FontFunctions.h"
+#include "mx/impl/IdFunctions.h"
 #include "mx/impl/LineFunctions.h"
 #include "mx/impl/MarkDataFunctions.h"
 #include "mx/impl/PrintFunctions.h"
@@ -165,6 +166,7 @@ std::vector<core::MusicDataChoice> DirectionWriter::getDirectionLikeThings()
     // nullopt for unspecified, and for the bottom-of-system values that only measure numbering has.
     // <harmony> carries the same attribute; createHarmonyElements writes it there too.
     direction.setSystem(myConverter.convertDirectionSystemRelation(myDirectionData.systemRelation));
+    setId(myDirectionData.id, direction);
 
     if (myDirectionData.isStaffValueSpecified || myCursor.staffIndex != 0)
     {
@@ -331,6 +333,7 @@ void DirectionWriter::emitPedal(const api::PedalLineData &item, core::Direction
     pedal.setType(corePedalType(item.kind));
     pedal.setLine(core::YesNo::yes());
     setAttributesFromPositionData(item.positionData, pedal);
+    setId(item.id, pedal);
     core::DirectionType dt{};
     dt.setChoice(core::DirectionTypeChoice::pedal(pedal));
     addDirectionType(std::move(dt), direction);
@@ -352,6 +355,7 @@ void DirectionWriter::emitWedgeStop(const api::WedgeStop &wedgeStop, const void
         wedge.setSpread(core::Tenths{core::Decimal{static_cast<double>(wedgeStop.spread)}});
     }
     setAttributesFromPositionData(wedgeStop.positionData, wedge);
+    setId(wedgeStop.id, wedge);
     core::DirectionType dt{};
     dt.setChoice(core::DirectionTypeChoice::wedge(wedge));
     addDirectionType(std::move(dt), direction);
@@ -384,6 +388,7 @@ void DirectionWriter::emitWedgeStart(const api::WedgeStart &wedgeStart, const vo
     {
         setAttributesFromColorData(wedgeStart.colorData, wedge);
     }
+    setId(wedgeStart.id, wedge);
     core::DirectionType dt{};
     dt.setChoice(core::DirectionTypeChoice::wedge(wedge));
     addDirectionType(std::move(dt), direction);
@@ -409,6 +414,7 @@ void DirectionWriter::emitOttavaStart(const api::OttavaStart &ottavaStart, const
     impl::setAttributesFromPositionData(ottavaStart.spannerStart.positionData, os);
     impl::setAttributesFromPrintData(ottavaStart.spannerStart.printData, os);
     impl::setAttributesFromLineData(ottavaStart.spannerStart.lineData, os);
+    impl::setId(ottavaStart.spannerStart.id, os);
 
     const auto number = myNumberResolver.emittedNumber(ottavaStart.spannerStart.number, inIdentity);
     if (number.has_value())
@@ -749,6 +755,7 @@ void DirectionWriter::emitWordsRun(const std::vector<api::WordsChoice> &inRun, c
             {
                 outSymbol.setJustify(myConverter.convert(symbolData.justify));
             }
+            setId(symbolData.id, outSymbol);
             choiceItem = core::DirectionTypeChoiceChoice::symbol(std::move(outSymbol));
         }
         else
@@ -770,6 +777,7 @@ void DirectionWriter::emitWordsRun(const std::vector<api::WordsChoice> &inRun, c
             {
                 outWords.setJustify(myConverter.convert(wordsData.justify));
             }
+            setId(wordsData.id, outWords);
             choiceItem = core::DirectionTypeChoiceChoice::words(std::move(outWords));
         }
 
@@ -851,6 +859,7 @@ void DirectionWriter::emitRehearsal(const api::RehearsalData &item, core::Direct
     {
         rehearsal.setJustify(myConverter.convert(item.justify));
     }
+    setId(item.id, rehearsal);
     core::DirectionType dt{};
     dt.setChoice(core::DirectionTypeChoice::rehearsal(core::OneOrMore<core::FormattedTextID>{std::move(rehearsal)}));
     addDirectionType(std::move(dt), direction);
@@ -1812,6 +1821,8 @@ std::vector<core::MusicDataChoice> DirectionWriter::createFiguredBassElements()
             }
         }
 
+        setId(figuredBassData.id, figuredBass);
+
         if (figuredBassData.parentheses != api::Bool::unspecified)
         {
             figuredBass.setParentheses(figuredBassData.parentheses == api::Bool::yes ? core::YesNo::yes()
diff --git a/src/private/mx/impl/IdFunctions.h b/src/private/mx/impl/IdFunctions.h
new file mode 100644
index 000000000..d3cda7b7c
--- /dev/null
+++ b/src/private/mx/impl/IdFunctions.h
@@ -0,0 +1,37 @@
+// MusicXML Class Library
+// Copyright (c) by Matthew James Briggs
+// Distributed under the MIT License
+
+#pragma once
+
+#include "mx/core/Token.h"
+
+#include <optional>
+#include <string>
+
+namespace mx
+{
+namespace impl
+{
+// Read the id attribute from any core element that has one. Absent stays absent.
+template <typename CORE_TYPE> std::optional<std::string> getId(const CORE_TYPE &inCoreElement)
+{
+    if (!inCoreElement.id().has_value())
+    {
+        return std::nullopt;
+    }
+
+    return inCoreElement.id()->value();
+}
+
+// Write the id attribute onto any core element that has one. An absent or empty id writes no
+// attribute. core::Token repairs an id that is not a valid XML name.
+template <typename CORE_TYPE> void setId(const std::optional<std::string> &inId, CORE_TYPE &outCoreElement)
+{
+    if (inId.has_value() && !inId->empty())
+    {
+        outCoreElement.setID(core::Token{*inId});
+    }
+}
+} // namespace impl
+} // namespace mx
diff --git a/src/private/mx/impl/MeasureReader.cpp b/src/private/mx/impl/MeasureReader.cpp
index d917b70a8..8adc66065 100644
--- a/src/private/mx/impl/MeasureReader.cpp
+++ b/src/private/mx/impl/MeasureReader.cpp
@@ -52,6 +52,7 @@
 #include "mx/core/generated/YesNo.h"
 #include "mx/impl/Converter.h"
 #include "mx/impl/DirectionReader.h"
+#include "mx/impl/IdFunctions.h"
 #include "mx/impl/NoteFunctions.h"
 #include "mx/impl/NoteReader.h"
 #include "mx/impl/SoundFunctions.h"
@@ -142,6 +143,7 @@ std::pair<api::MeasureData, std::optional<api::TransposeData>> MeasureReader::ge
     std::lock_guard<std::mutex> lock(myMutex);
     myOutMeasureData = api::MeasureData{};
     myOutMeasureData.number = myPartwiseMeasure.number();
+    myOutMeasureData.id = getId(myPartwiseMeasure);
 
     // if we are parsing the first measure of the part, then we need to return transpose information
     std::optional<api::TransposeData> transpose;
@@ -234,10 +236,13 @@ void MeasureReader::parseTimeSignature() const
         staffTimeSignatures = myPreviousMeasureCursor.staffTimeSignatures;
     }
 
+    // A carried-forward time signature is not the <time> element that stated it, so it keeps no id.
     timeSignature.isImplicit = true;
+    timeSignature.id.reset();
     for (auto &entry : staffTimeSignatures)
     {
         entry.second.isImplicit = true;
+        entry.second.id.reset();
     }
 
     TimeReader timeReader{myPartwiseMeasure.musicData()};
@@ -684,6 +689,7 @@ std::optional<api::TransposeData> MeasureReader::parseAttributes(const core::Att
                 keyData.nonTraditional.emplace_back(keyComponent);
             }
 
+            keyData.id = getId(key);
             myOutMeasureData.keys.emplace_back(std::move(keyData));
             continue;
         }
@@ -716,6 +722,7 @@ std::optional<api::TransposeData> MeasureReader::parseAttributes(const core::Att
             keyData.mode = myConverter.convert(*traditionalKey.mode());
         }
         keyData.tickTimePosition = myCurrentCursor.tickTimePosition;
+        keyData.id = getId(key);
 
         myOutMeasureData.keys.emplace_back(std::move(keyData));
     }
@@ -766,6 +773,7 @@ std::optional<api::TransposeData> MeasureReader::parseAttributes(const core::Att
             }
 
             transposeData.tickTimePosition = myCurrentCursor.tickTimePosition;
+            transposeData.id = getId(coreTranspose);
             myOutMeasureData.transpositions.emplace_back(std::move(transposeData));
         }
     }
@@ -829,6 +837,8 @@ void MeasureReader::parseFiguredBass(const core::FiguredBass &inMxFiguredBass, c
         figuredBass.durationTimeTicks = myCurrentCursor.convertDurationToGlobalTickScale(*inMxFiguredBass.duration());
     }
 
+    figuredBass.id = getId(inMxFiguredBass);
+
     auto direction = api::DirectionData{};
     direction.tickTimePosition = myCurrentCursor.tickTimePosition;
     direction.placement = api::Placement::below;
@@ -978,6 +988,7 @@ void MeasureReader::parseBarline(const core::Barline &inMxBarline) const
     barline.repeatDirection = repeatDirection;
     barline.repeatAfterJump = repeatAfterJump;
     barline.repeatWinged = repeatWinged;
+    barline.id = getId(inMxBarline);
     myOutMeasureData.barlines.emplace_back(std::move(barline));
 }
 
@@ -1047,6 +1058,7 @@ void MeasureReader::importClef(const core::Clef &inClef) const
 {
     api::ClefData clefData;
     clefData.tickTimePosition = myCurrentCursor.tickTimePosition;
+    clefData.id = getId(inClef);
     auto converter = Converter{};
     clefData.symbol = converter.convert(inClef.clef().sign());
 
diff --git a/src/private/mx/impl/MeasureWriter.cpp b/src/private/mx/impl/MeasureWriter.cpp
index 4ff2bf2ad..b099084eb 100644
--- a/src/private/mx/impl/MeasureWriter.cpp
+++ b/src/private/mx/impl/MeasureWriter.cpp
@@ -35,6 +35,7 @@
 #include "mx/core/generated/YesNo.h"
 #include "mx/impl/Converter.h"
 #include "mx/impl/DirectionWriter.h"
+#include "mx/impl/IdFunctions.h"
 #include "mx/impl/LayoutFunctions.h"
 #include "mx/impl/NoteWriter.h"
 #include "mx/impl/ScoreWriter.h"
@@ -100,6 +101,8 @@ void MeasureWriter::writeMeasureGlobals()
         myOutMeasure.setWidth(core::Tenths{core::Decimal{static_cast<double>(myMeasureData.width)}});
     }
 
+    impl::setId(myMeasureData.id, myOutMeasure);
+
     Converter converter;
 
     if (myMeasureData.implicit != api::Bool::unspecified)
@@ -916,6 +919,7 @@ void MeasureWriter::writeBarlines(int tickTimePosition)
             barlineElement.setRepeat(repeatElement);
         }
 
+        impl::setId(myBarlinesIter->id, barlineElement);
         myOutMeasure.addMusicData(core::MusicDataChoice::barline(barlineElement));
         myHistory.log("writeBarline");
     }
diff --git a/src/private/mx/impl/NotationsWriter.cpp b/src/private/mx/impl/NotationsWriter.cpp
index 6973c3b25..f79da2233 100644
--- a/src/private/mx/impl/NotationsWriter.cpp
+++ b/src/private/mx/impl/NotationsWriter.cpp
@@ -62,6 +62,7 @@
 #include "mx/impl/Converter.h"
 #include "mx/impl/CurveFunctions.h"
 #include "mx/impl/DynamicsWriter.h"
+#include "mx/impl/IdFunctions.h"
 #include "mx/impl/MarkDataFunctions.h"
 #include "mx/impl/PositionFunctions.h"
 #include "mx/impl/ScoreWriter.h"
@@ -184,6 +185,7 @@ core::Notations NotationsWriter::getNotations() const
     {
         core::Tuplet tuplet;
         tuplet.setType(core::StartStop::stop());
+        setId(tupletStop.id, tuplet);
 
         if (tupletStop.numberLevel > 0)
         {
@@ -197,6 +199,7 @@ core::Notations NotationsWriter::getNotations() const
     {
         core::Tuplet tuplet;
         tuplet.setType(core::StartStop::start());
+        setId(tupletStart.id, tuplet);
 
         core::TupletPortion actual;
         core::TupletNumber tn1;
diff --git a/src/private/mx/impl/NoteFunctions.cpp b/src/private/mx/impl/NoteFunctions.cpp
index 8ca73c289..705c715df 100644
--- a/src/private/mx/impl/NoteFunctions.cpp
+++ b/src/private/mx/impl/NoteFunctions.cpp
@@ -11,6 +11,7 @@
 #include "mx/impl/CurveFunctions.h"
 #include "mx/impl/DynamicsReader.h"
 #include "mx/impl/FermataFunctions.h"
+#include "mx/impl/IdFunctions.h"
 #include "mx/impl/MarkDataFunctions.h"
 #include "mx/impl/NonArpeggiateFunctions.h"
 #include "mx/impl/NoteReader.h"
@@ -159,6 +160,7 @@ api::NoteData NoteFunctions::parseNote() const
 
     parseMiscData();
     myOutNoteData.positionData = impl::getPositionData(myNote);
+    myOutNoteData.id = impl::getId(myNote);
 
     return myOutNoteData;
 }
diff --git a/src/private/mx/impl/NoteReader.cpp b/src/private/mx/impl/NoteReader.cpp
index d95270a18..c714ec141 100644
--- a/src/private/mx/impl/NoteReader.cpp
+++ b/src/private/mx/impl/NoteReader.cpp
@@ -15,6 +15,7 @@
 #include "mx/core/generated/TextElementData.h"
 #include "mx/core/generated/Tied.h"
 #include "mx/impl/FontFunctions.h"
+#include "mx/impl/IdFunctions.h"
 #include "mx/impl/PositionFunctions.h"
 #include "mx/impl/PrintFunctions.h"
 #include "mx/utility/StringToInt.h"
@@ -527,6 +528,7 @@ void NoteReader::setLyric()
 
         api::LyricData lyricData;
         lyricData.positionData = getLyricPositionData(lyric);
+        lyricData.id = getId(lyric);
 
         if (lyric.number().has_value())
         {
diff --git a/src/private/mx/impl/NoteWriter.cpp b/src/private/mx/impl/NoteWriter.cpp
index 90f6b18b3..9ed71c384 100644
--- a/src/private/mx/impl/NoteWriter.cpp
+++ b/src/private/mx/impl/NoteWriter.cpp
@@ -27,6 +27,7 @@
 #include "mx/core/generated/TimeModification.h"
 #include "mx/core/generated/TimeModificationGroup.h"
 #include "mx/core/generated/Unpitched.h"
+#include "mx/impl/IdFunctions.h"
 #include "mx/impl/NotationsWriter.h"
 #include "mx/impl/PositionFunctions.h"
 #include "mx/impl/PrintFunctions.h"
@@ -85,6 +86,7 @@ core::Note NoteWriter::getNote(bool isStartOfChord) const
     setNotehead();
     setStemDirection();
     setMiscData();
+    impl::setId(myNoteData.id, myOutNote);
     NotationsWriter notationsWriter{myNoteData, myCursor, myScoreWriter};
     impl::setAttributesFromPositionData(myNoteData.positionData, myOutNote);
     if (myNoteData.printData.printObject != api::Bool::unspecified)
@@ -559,6 +561,7 @@ void NoteWriter::setLyrics() const
         }
 
         impl::setAttributesFromPositionData(lyricData.positionData, lyric);
+        impl::setId(lyricData.id, lyric);
         if (lyricData.positionData.horizontalAlignment != api::HorizontalAlignment::unspecified)
         {
             lyric.setJustify(myConverter.convert(lyricData.positionData.horizontalAlignment));
diff --git a/src/private/mx/impl/PropertiesWriter.cpp b/src/private/mx/impl/PropertiesWriter.cpp
index b80a5faf9..99bbe0a0d 100644
--- a/src/private/mx/impl/PropertiesWriter.cpp
+++ b/src/private/mx/impl/PropertiesWriter.cpp
@@ -40,6 +40,7 @@
 #include "mx/core/generated/Transpose.h"
 #include "mx/core/generated/YesNo.h"
 #include "mx/impl/Converter.h"
+#include "mx/impl/IdFunctions.h"
 
 namespace mx
 {
@@ -94,6 +95,7 @@ void PropertiesWriter::writeMultipleRest(int measureCount, api::Bool useSymbols)
 void PropertiesWriter::writeKey(int staffIndex, const api::KeyData &inKeyData)
 {
     core::Key key{};
+    impl::setId(inKeyData.id, key);
 
     if (staffIndex >= 0)
     {
@@ -234,6 +236,7 @@ void PropertiesWriter::writeTime(const api::TimeChoice &value, int staffIndex)
 {
     Converter converter;
     core::Time time{};
+    impl::setId(value.id, time);
 
     if (value.isSimple())
     {
@@ -325,6 +328,7 @@ void PropertiesWriter::writeStaffDetails(int staffIndex, int staffLines, double
 void PropertiesWriter::writeClef(int staffIndex, const api::ClefData &inClefData)
 {
     core::Clef mxClef{};
+    impl::setId(inClefData.id, mxClef);
 
     // staffIndex < 0 means a single-staff part (the caller's clefStaffIndex() collapses it), so the
     // auto rule omits the implied 1; staffIndex >= 0 is a multi-staff part, so the auto rule emits
@@ -403,6 +407,7 @@ void PropertiesWriter::writePartSymbol(const api::PartSymbolData &inPartSymbolDa
 void PropertiesWriter::writeTranspose(int staffIndex, const api::TransposeData &inTransposeData)
 {
     auto xpose = Converter::convertToTranspose(inTransposeData);
+    impl::setId(inTransposeData.id, xpose);
 
     if (staffIndex >= 0)
     {
diff --git a/src/private/mx/impl/SoundFunctions.cpp b/src/private/mx/impl/SoundFunctions.cpp
index b1f0c1995..a9f94f851 100644
--- a/src/private/mx/impl/SoundFunctions.cpp
+++ b/src/private/mx/impl/SoundFunctions.cpp
@@ -12,6 +12,7 @@
 #include "mx/core/generated/SwingChoiceGroup.h"
 #include "mx/core/generated/SwingTypeValue.h"
 #include "mx/core/generated/YesNo.h"
+#include "mx/impl/IdFunctions.h"
 
 namespace mx
 {
@@ -144,11 +145,15 @@ api::SoundData readSoundData(const core::Sound &inSound)
         out.swing = soundFunctionsToApiSwingData(*inSound.swing());
     }
 
+    out.id = getId(inSound);
+
     return out;
 }
 
 void writeSoundData(const api::SoundData &inSoundData, core::Sound &outSound)
 {
+    setId(inSoundData.id, outSound);
+
     if (inSoundData.tempo >= 0.0)
     {
         outSound.setTempo(core::NonNegativeDecimal{core::Decimal{inSoundData.tempo}});
diff --git a/src/private/mx/impl/SpannerFunctions.h b/src/private/mx/impl/SpannerFunctions.h
index 4116cd199..1baa8cc4a 100644
--- a/src/private/mx/impl/SpannerFunctions.h
+++ b/src/private/mx/impl/SpannerFunctions.h
@@ -5,10 +5,10 @@
 #pragma once
 
 #include "mx/api/SpannerData.h"
+#include "mx/impl/IdFunctions.h"
 #include "mx/impl/LineFunctions.h"
 #include "mx/impl/PositionFunctions.h"
 #include "mx/impl/PrintFunctions.h"
-#include "mx/utility/Unused.h"
 
 #include <optional>
 
@@ -29,6 +29,7 @@ template <typename ATTRIBUTES_TYPE> api::SpannerStart getSpannerStart(const ATTR
     start.positionData = getPositionData(inAttributes);
     start.printData = getPrintData(inAttributes);
     start.lineData = getLineData(inAttributes);
+    start.id = getId(inAttributes);
     return start;
 }
 
@@ -41,6 +42,7 @@ template <typename ATTRIBUTES_TYPE> api::SpannerStop getSpannerStop(const ATTRIB
     }
     stop.positionData = getPositionData(inAttributes);
     stop.lineData = getLineData(inAttributes);
+    stop.id = getId(inAttributes);
     return stop;
 }
 
@@ -53,7 +55,8 @@ template <typename ATTRIBUTES_TYPE>
 void setAttributesFromSpannerStart(const api::SpannerStart &start, ATTRIBUTES_TYPE &outAttributes,
                                    const std::optional<int> &inResolvedNumber)
 {
-    MX_UNUSED(start);
+    setId(start.id, outAttributes);
+
     if (inResolvedNumber.has_value())
     {
         lookForAndSetHasNumber(true, &outAttributes);
@@ -81,6 +84,7 @@ void setAttributesFromSpannerStop(const api::SpannerStop &stop, ATTRIBUTES_TYPE
 
     setAttributesFromPositionData(stop.positionData, outAttributes);
     setAttributesFromLineData(stop.lineData, outAttributes);
+    setId(stop.id, outAttributes);
 }
 } // namespace impl
 } // namespace mx
diff --git a/src/private/mx/impl/TimeReader.cpp b/src/private/mx/impl/TimeReader.cpp
index b412bfd71..f94bbd577 100644
--- a/src/private/mx/impl/TimeReader.cpp
+++ b/src/private/mx/impl/TimeReader.cpp
@@ -11,6 +11,7 @@
 #include "mx/core/generated/TimeChoiceGroup.h"
 #include "mx/core/generated/TimeSignatureGroup.h"
 #include "mx/impl/Converter.h"
+#include "mx/impl/IdFunctions.h"
 
 #include <utility>
 #include <vector>
@@ -100,6 +101,7 @@ TimeReaderResult TimeReader::createTimeChoice(const core::Time &inTime)
     }
 
     timeChoice.isImplicit = false;
+    timeChoice.id = getId(inTime);
     if (inTime.printObject().has_value())
     {
         timeChoice.display = converter.convert(*inTime.printObject());
diff --git a/src/private/mx/impl/TupletReader.cpp b/src/private/mx/impl/TupletReader.cpp
index 12605fdf6..900a94457 100644
--- a/src/private/mx/impl/TupletReader.cpp
+++ b/src/private/mx/impl/TupletReader.cpp
@@ -9,6 +9,7 @@
 #include "mx/core/generated/Tuplet.h"
 #include "mx/core/generated/TupletPortion.h"
 #include "mx/impl/Converter.h"
+#include "mx/impl/IdFunctions.h"
 #include "mx/impl/MarkDataFunctions.h"
 
 namespace mx
@@ -25,6 +26,7 @@ void TupletReader::parseTuplet(std::vector<api::TupletStart> &outTupletStarts,
 {
     api::TupletStart tupletStart;
     tupletStart.positionData = impl::getPositionData(myTuplet);
+    tupletStart.id = getId(myTuplet);
 
     if (myTuplet.number().has_value())
     {
@@ -36,6 +38,7 @@ void TupletReader::parseTuplet(std::vector<api::TupletStart> &outTupletStarts,
         api::TupletStop tupletStop;
         tupletStop.positionData = tupletStart.positionData;
         tupletStop.numberLevel = tupletStart.numberLevel;
+        tupletStop.id = getId(myTuplet);
         outTupletStops.emplace_back(std::move(tupletStop));
         return;
     }
diff --git a/src/private/mxtest/api/IdAttributeApiTest.cpp b/src/private/mxtest/api/IdAttributeApiTest.cpp
new file mode 100644
index 000000000..c9d3ed7eb
--- /dev/null
+++ b/src/private/mxtest/api/IdAttributeApiTest.cpp
@@ -0,0 +1,429 @@
+// MusicXML Class Library
+// Copyright (c) by Matthew James Briggs
+// Distributed under the MIT License
+
+#include "mxtest/control/CompileControl.h"
+#ifdef MX_COMPILE_API_TESTS
+
+#include "cpul/cpulTestHarness.h"
+#include "mx/api/DocumentManager.h"
+#include "mx/api/ScoreData.h"
+#include "mxtest/api/RoundTrip.h"
+#include "mxtest/api/TestHelpers.h"
+
+using namespace std;
+using namespace mx::api;
+using namespace mxtest;
+
+// A one-part, one-measure score holding a single quarter note, ready for a test to hang ids on.
+static ScoreData idAttributeMakeScore()
+{
+    ScoreData score;
+    score.ticksPerQuarter = 4;
+    score.parts.emplace_back();
+    auto &part = score.parts.back();
+    part.name = "P1";
+    part.uniqueId = "P1";
+    part.measures.emplace_back();
+    auto &measure = part.measures.back();
+    measure.staves.emplace_back();
+    auto &staff = measure.staves.back();
+
+    NoteData note{};
+    note.pitchData.step = Step::c;
+    note.pitchData.octave = 4;
+    note.durationData.durationTimeTicks = 4;
+    note.durationData.durationName = DurationName::quarter;
+    note.tickTimePosition = 0;
+    staff.voices[0].notes.push_back(note);
+
+    return score;
+}
+
+static MeasureData &idAttributeMeasure(ScoreData &score)
+{
+    return score.parts.back().measures.back();
+}
+
+static const MeasureData &idAttributeMeasure(const ScoreData &score)
+{
+    return score.parts.back().measures.back();
+}
+
+static NoteData &idAttributeNote(ScoreData &score)
+{
+    return idAttributeMeasure(score).staves.back().voices.at(0).notes.back();
+}
+
+static const NoteData &idAttributeNote(const ScoreData &score)
+{
+    return idAttributeMeasure(score).staves.back().voices.at(0).notes.back();
+}
+
+// The <note> id, the reason for issue 399, plus the <measure> and <lyric> ids around it.
+TEST(noteMeasureAndLyricIds, IdAttribute)
+{
+    auto score = idAttributeMakeScore();
+    idAttributeMeasure(score).id = "m1";
+
+    auto &note = idAttributeNote(score);
+    note.id = "n1";
+
+    LyricData lyric;
+    lyric.text = "la";
+    lyric.id = "ly1";
+    note.lyrics.push_back(lyric);
+
+    const auto xml = toXml(score);
+    CHECK(xml.find("id=\"n1\"") != std::string::npos);
+
+    const auto out = roundTrip(score);
+    CHECK(std::optional<std::string>{"m1"} == idAttributeMeasure(out).id);
+
+    const auto &onote = idAttributeNote(out);
+    CHECK(std::optional<std::string>{"n1"} == onote.id);
+    REQUIRE(onote.lyrics.size() == 1);
+    CHECK(std::optional<std::string>{"ly1"} == onote.lyrics.front().id);
+}
+
+T_END;
+
+// The ids on the elements that live in <attributes>, plus the <barline> id.
+TEST(attributesAndBarlineIds, IdAttribute)
+{
+    auto score = idAttributeMakeScore();
+    auto &measure = idAttributeMeasure(score);
+
+    measure.timeSignature = TimeChoice{TimeSignatureData{}};
+    measure.timeSignature.isImplicit = false;
+    measure.timeSignature.id = "t1";
+
+    KeyData key;
+    key.fifths = 2;
+    key.mode = KeyMode::major;
+    key.id = "k1";
+    measure.keys.push_back(key);
+
+    ClefData clef;
+    clef.setTreble();
+    clef.id = "c1";
+    measure.staves.back().clefs.push_back(clef);
+
+    TransposeData transpose{-2, -1};
+    transpose.id = "x1";
+    measure.transpositions.push_back(transpose);
+
+    BarlineData barline;
+    barline.barlineType = BarlineType::lightHeavy;
+    barline.location = HorizontalAlignment::right;
+    barline.id = "b1";
+    measure.barlines.push_back(barline);
+
+    const auto out = roundTrip(score);
+    const auto &omeasure = idAttributeMeasure(out);
+
+    CHECK(std::optional<std::string>{"t1"} == omeasure.timeSignature.id);
+    REQUIRE(omeasure.keys.size() == 1);
+    CHECK(std::optional<std::string>{"k1"} == omeasure.keys.front().id);
+    REQUIRE(omeasure.staves.back().clefs.size() == 1);
+    CHECK(std::optional<std::string>{"c1"} == omeasure.staves.back().clefs.front().id);
+    REQUIRE(omeasure.transpositions.size() == 1);
+    CHECK(std::optional<std::string>{"x1"} == omeasure.transpositions.front().id);
+    REQUIRE(omeasure.barlines.size() == 1);
+    CHECK(std::optional<std::string>{"b1"} == omeasure.barlines.front().id);
+}
+
+T_END;
+
+// A time signature that a later measure inherits carries no id: only the measure that states the
+// <time> element owns it.
+TEST(inheritedTimeSignatureHasNoId, IdAttribute)
+{
+    auto score = idAttributeMakeScore();
+    auto &measure = idAttributeMeasure(score);
+    measure.timeSignature = TimeChoice{TimeSignatureData{}};
+    measure.timeSignature.isImplicit = false;
+    measure.timeSignature.id = "t1";
+
+    auto &part = score.parts.back();
+    part.measures.push_back(part.measures.back());
+    part.measures.back().timeSignature.isImplicit = true;
+    part.measures.back().id = std::nullopt;
+
+    const auto out = roundTrip(score);
+    REQUIRE(out.parts.back().measures.size() == 2);
+    CHECK(std::optional<std::string>{"t1"} == out.parts.back().measures.front().timeSignature.id);
+    CHECK(!out.parts.back().measures.back().timeSignature.id.has_value());
+}
+
+T_END;
+
+// The <direction> id and the ids of the direction-type elements mx::api models as their own types.
+TEST(directionIds, IdAttribute)
+{
+    auto score = idAttributeMakeScore();
+    auto &staff = idAttributeMeasure(score).staves.back();
+
+    DirectionData direction;
+    direction.tickTimePosition = 0;
+    direction.id = "d1";
+
+    WordsData words;
+    words.text = "dolce";
+    words.id = "w1";
+
+    SymbolData symbol;
+    symbol.smufl = "arrowBlackUp";
+    symbol.id = "sy1";
+
+    direction.directionTypes.emplace_back(
+        DirectionChoice{std::vector<WordsChoice>{WordsChoice{words}, WordsChoice{symbol}}});
+
+    RehearsalData rehearsal;
+    rehearsal.text = "A";
+    rehearsal.id = "r1";
+    direction.directionTypes.emplace_back(DirectionChoice{rehearsal});
+
+    WedgeStart wedgeStart;
+    wedgeStart.wedgeType = WedgeType::crescendo;
+    wedgeStart.id = "we1";
+    direction.directionTypes.emplace_back(DirectionChoice{wedgeStart});
+
+    SpannerStart bracketStart;
+    bracketStart.id = "br1";
+    direction.directionTypes.emplace_back(DirectionChoice::bracketStart(bracketStart));
+
+    SpannerStart dashesStart;
+    dashesStart.id = "da1";
+    direction.directionTypes.emplace_back(DirectionChoice::dashesStart(dashesStart));
+
+    OttavaStart ottavaStart;
+    ottavaStart.ottavaType = OttavaType::o8va;
+    ottavaStart.spannerStart.id = "o1";
+    direction.directionTypes.emplace_back(DirectionChoice{ottavaStart});
+
+    PedalLineData pedal{PedalLineKind::start};
+    pedal.id = "p1";
+    direction.directionTypes.emplace_back(DirectionChoice{pedal});
+
+    direction.isSoundDataSpecified = true;
+    direction.soundData.tempo = 120.0;
+    direction.soundData.id = "so1";
+
+    staff.directions.push_back(direction);
+
+    const auto out = roundTrip(score);
+    const auto &odirections = idAttributeMeasure(out).staves.back().directions;
+    REQUIRE(odirections.size() == 1);
+    const auto &odirection = odirections.front();
+
+    CHECK(std::optional<std::string>{"d1"} == odirection.id);
+    CHECK(std::optional<std::string>{"so1"} == odirection.soundData.id);
+
+    std::optional<std::string> foundWords;
+    std::optional<std::string> foundSymbol;
+    std::optional<std::string> foundRehearsal;
+    std::optional<std::string> foundWedge;
+    std::optional<std::string> foundBracket;
+    std::optional<std::string> foundDashes;
+    std::optional<std::string> foundOttava;
+    std::optional<std::string> foundPedal;
+
+    for (const auto &choice : odirection.directionTypes)
+    {
+        switch (choice.kind())
+        {
+        case DirectionChoice::Kind::wordsRun:
+            for (const auto &item : choice.wordsRun())
+            {
+                if (item.isWords())
+                {
+                    foundWords = item.words().id;
+                }
+                else if (item.isSymbol())
+                {
+                    foundSymbol = item.symbol().id;
+                }
+            }
+            break;
+        case DirectionChoice::Kind::rehearsal:
+            foundRehearsal = choice.rehearsal().id;
+            break;
+        case DirectionChoice::Kind::wedgeStart:
+            foundWedge = choice.wedgeStart().id;
+            break;
+        case DirectionChoice::Kind::bracketStart:
+            foundBracket = choice.bracketStart().id;
+            break;
+        case DirectionChoice::Kind::dashesStart:
+            foundDashes = choice.dashesStart().id;
+            break;
+        case DirectionChoice::Kind::ottavaStart:
+            foundOttava = choice.ottavaStart().spannerStart.id;
+            break;
+        case DirectionChoice::Kind::pedal:
+            foundPedal = choice.pedal().id;
+            break;
+        default:
+            break;
+        }
+    }
+
+    CHECK(std::optional<std::string>{"w1"} == foundWords);
+    CHECK(std::optional<std::string>{"sy1"} == foundSymbol);
+    CHECK(std::optional<std::string>{"r1"} == foundRehearsal);
+    CHECK(std::optional<std::string>{"we1"} == foundWedge);
+    CHECK(std::optional<std::string>{"br1"} == foundBracket);
+    CHECK(std::optional<std::string>{"da1"} == foundDashes);
+    CHECK(std::optional<std::string>{"o1"} == foundOttava);
+    CHECK(std::optional<std::string>{"p1"} == foundPedal);
+}
+
+T_END;
+
+// The ids on the note-attached elements: <slur>, <tuplet> and a let-ring <tied>.
+TEST(notationIds, IdAttribute)
+{
+    auto score = idAttributeMakeScore();
+    auto &staff = idAttributeMeasure(score).staves.back();
+    auto &notes = staff.voices.at(0).notes;
+
+    NoteData second = notes.back();
+    second.tickTimePosition = 4;
+    notes.push_back(second);
+
+    CurveStart slurStart{CurveType::slur};
+    slurStart.id = "s1";
+    notes.front().noteAttachmentData.curveStarts.push_back(slurStart);
+
+    CurveStop slurStop{CurveType::slur};
+    slurStop.id = "s2";
+    notes.back().noteAttachmentData.curveStops.push_back(slurStop);
+
+    TupletStart tupletStart;
+    tupletStart.actualNumber = 3;
+    tupletStart.actualDurationName = DurationName::quarter;
+    tupletStart.normalNumber = 2;
+    tupletStart.normalDurationName = DurationName::quarter;
+    tupletStart.id = "tu1";
+    notes.front().noteAttachmentData.tupletStarts.push_back(tupletStart);
+
+    TupletStop tupletStop;
+    tupletStop.id = "tu2";
+    notes.back().noteAttachmentData.tupletStops.push_back(tupletStop);
+
+    TieLetRing letRing;
+    letRing.id = "lr1";
+    notes.back().tieLetRing = letRing;
+
+    const auto out = roundTrip(score);
+    const auto &onotes = idAttributeMeasure(out).staves.back().voices.at(0).notes;
+    REQUIRE(onotes.size() == 2);
+
+    REQUIRE(onotes.front().noteAttachmentData.curveStarts.size() == 1);
+    CHECK(std::optional<std::string>{"s1"} == onotes.front().noteAttachmentData.curveStarts.front().id);
+    REQUIRE(onotes.back().noteAttachmentData.curveStops.size() == 1);
+    CHECK(std::optional<std::string>{"s2"} == onotes.back().noteAttachmentData.curveStops.front().id);
+
+    REQUIRE(onotes.front().noteAttachmentData.tupletStarts.size() == 1);
+    CHECK(std::optional<std::string>{"tu1"} == onotes.front().noteAttachmentData.tupletStarts.front().id);
+    REQUIRE(onotes.back().noteAttachmentData.tupletStops.size() == 1);
+    CHECK(std::optional<std::string>{"tu2"} == onotes.back().noteAttachmentData.tupletStops.front().id);
+
+    REQUIRE(onotes.back().tieLetRing.has_value());
+    CHECK(std::optional<std::string>{"lr1"} == onotes.back().tieLetRing->id);
+}
+
+T_END;
+
+// The <figured-bass> id.
+TEST(figuredBassId, IdAttribute)
+{
+    auto score = idAttributeMakeScore();
+    auto &staff = idAttributeMeasure(score).staves.back();
+
+    FigureData figure;
+    figure.figureNumber = "6";
+
+    FiguredBassData figuredBass;
+    figuredBass.figures.push_back(figure);
+    figuredBass.id = "fb1";
+
+    DirectionData direction;
+    direction.tickTimePosition = 0;
+    direction.placement = Placement::below;
+    direction.figuredBasses.push_back(figuredBass);
+    staff.directions.push_back(direction);
+
+    const auto out = roundTrip(score);
+    const auto &odirections = idAttributeMeasure(out).staves.back().directions;
+    REQUIRE(odirections.size() == 1);
+    REQUIRE(odirections.front().figuredBasses.size() == 1);
+    CHECK(std::optional<std::string>{"fb1"} == odirections.front().figuredBasses.front().id);
+}
+
+T_END;
+
+// Reading ids straight off a MusicXML source.
+TEST(idsAreReadFromSourceXml, IdAttribute)
+{
+    const std::string xml = R"(<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE score-partwise PUBLIC "-//Recordare//DTD MusicXML 4.0 Partwise//EN" "http://www.musicxml.org/dtds/partwise.dtd">
+<score-partwise version="4.0">
+  <part-list>
+    <score-part id="P1">
+      <part-name>Music</part-name>
+    </score-part>
+  </part-list>
+  <part id="P1">
+    <measure number="1" id="m1">
+      <attributes>
+        <divisions>1</divisions>
+        <key id="k1">
+          <fifths>0</fifths>
+        </key>
+        <time id="t1">
+          <beats>4</beats>
+          <beat-type>4</beat-type>
+        </time>
+        <clef id="c1">
+          <sign>G</sign>
+          <line>2</line>
+        </clef>
+      </attributes>
+      <note id="n1">
+        <pitch>
+          <step>C</step>
+          <octave>4</octave>
+        </pitch>
+        <duration>4</duration>
+        <type>whole</type>
+      </note>
+      <barline location="right" id="b1">
+        <bar-style>light-heavy</bar-style>
+      </barline>
+    </measure>
+  </part>
+</score-partwise>)";
+
+    const auto score = fromXml(xml);
+    REQUIRE(score.parts.size() == 1);
+    const auto &measure = score.parts.front().measures.front();
+
+    CHECK(std::optional<std::string>{"m1"} == measure.id);
+    CHECK(std::optional<std::string>{"t1"} == measure.timeSignature.id);
+    REQUIRE(measure.keys.size() == 1);
+    CHECK(std::optional<std::string>{"k1"} == measure.keys.front().id);
+    REQUIRE(measure.staves.front().clefs.size() == 1);
+    CHECK(std::optional<std::string>{"c1"} == measure.staves.front().clefs.front().id);
+    REQUIRE(measure.barlines.size() == 1);
+    CHECK(std::optional<std::string>{"b1"} == measure.barlines.front().id);
+
+    const auto &notes = measure.staves.front().voices.at(0).notes;
+    REQUIRE(notes.size() == 1);
+    CHECK(std::optional<std::string>{"n1"} == notes.front().id);
+}
+
+T_END;
+
+#endif
diff --git a/src/private/mxtest/api/roundtrip-baseline.txt b/src/private/mxtest/api/roundtrip-baseline.txt
index 72a311cac..26ce9b255 100644
--- a/src/private/mxtest/api/roundtrip-baseline.txt
+++ b/src/private/mxtest/api/roundtrip-baseline.txt
@@ -639,3 +639,8 @@ synthetic/harmonic.3.0.xml
 # attribute: this file's number="1, 2, 3" came back as number="1". BarlineData::ending
 # is now an optional EndingData holding the whole number list plus the display text.
 lysuite/ly45f_Repeats_InvalidEndings.xml
+
+# Unblocked by #399 (MusicXML id attributes). The id attribute of <bracket> and
+# <dashes> reaches the api on SpannerStart/SpannerStop, so it is no longer dropped.
+synthetic/bracket.3.1.xml
+synthetic/dashes.3.1.xml