diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..3d8971c
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,12 @@
+/vendor
+_*
+go.sum
+go.sum
+go.work
+vendor/
+_*
+benchmark*
+.claude*
+claude*
+CLAUDE*
+coverage*
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 673382f..e33598c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,26 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - **Minor**: feature additions, removal of deprecated features
 - **Patch**: bug fixes, backward compatible protobuf model changes, etc.
 
+# v2.2.0 - 2026-05-23
+#### Added
+* `model.Model.GetData()` — returns snapshots of the data set and key/index maps; implementations must not expose internal storage directly
+* `model.Model.Reverse()` — reverses the order of the data store
+* `sorter.SortByValue` — zero-value `SortFlag`; type-stratified sort (nil < bool < numeric < string < other); now the default sort behavior
+* `sorter.SortAsc`, `SortDesc`, `SortAsString`, `SortReverse` — explicit bitflag sort options
+* `.gitignore`
+
+#### Changed
+* `model.ModelTypeHash` / `model.ModelTypeList` renamed to `model.HASH` / `model.LIST`; order swapped so `HASH` is the zero/iota value
+* `model.Model.Filter` callback signature changed from `func(Value) Model` to `func(Value) bool`
+* `model.Model.Map` callback signature changed from `func(Value) Model` to `func(Value) Value`
+* `model.Model.Reduce` callback signature changed from `func(Value) bool` to `func(carry, cur Value) Value` (standard fold semantics)
+* `model.Model.SetID` now returns `error`
+* `sorter.SortFlag` underlying type changed from `int` to `uint`
+* `sorter.Sorter.Reverse` signature changed from `Reverse(SortFlag) error` to `Reverse() error`
+
+#### Fixed
+* `errors/error.go` package declaration corrected from `package error` to `package errors`
+
 # v2.1.0 - 2020-05-30
 #### Added
 * `Caller` package
diff --git a/errors/error.go b/errors/error.go
index bb44660..2b07943 100644
--- a/errors/error.go
+++ b/errors/error.go
@@ -1,4 +1,4 @@
-package error
+package errors
 
 import (
 	"github.com/bdlm/std/v2/caller"
diff --git a/model/model.go b/model/model.go
index 8438c46..1827285 100644
--- a/model/model.go
+++ b/model/model.go
@@ -4,12 +4,13 @@ package model
 type ModelType int
 
 const (
-	// ModelTypeList causes the model to behave as a list (keys are unsigned,
-	// contiguous integers beginning at 0).
-	ModelTypeList ModelType = iota
-	// ModelTypeHash causes the model to behave as a hash (keys are strings,
+	// HASH causes the model to behave as a hash (keys are strings,
 	// order is static).
-	ModelTypeHash
+	HASH ModelType = iota
+
+	// LIST causes the model to behave as a list (keys are unsigned,
+	// contiguous integers beginning at 0).
+	LIST
 )
 
 // Model is a list or a map of Values.
@@ -23,10 +24,23 @@ type Model interface {
 	Delete(key interface{}) error
 	// Filter filters elements of the data using a callback function and
 	// returns the result.
-	Filter(callback func(Value) Model) Model
+	Filter(callback func(Value) bool) Model
 	// Get returns the specified data value in this model.
 	Get(key interface{}) (Value, error)
-	// GetID returns returns this model's id.
+	// GetData returns snapshots of the current data set and indexes.
+	//
+	// Implementations must not expose internal slice or map storage directly;
+	// the returned slice and maps must be safe for the caller to read and
+	// modify without affecting the model's internal state.
+	//
+	// The return values are:
+	//   - data: a snapshot of the model's values in model order.
+	//   - keyToIndex: a snapshot of hash keys to indexes for HASH models; nil
+	//     for LIST models.
+	//   - indexToKey: a snapshot of indexes to hash keys for HASH models; nil
+	//     for LIST models.
+	GetData() ([]interface{}, map[string]int, map[int]string)
+	// GetID returns this model's id.
 	GetID() interface{}
 	// GetType returns the model type.
 	GetType() ModelType
@@ -36,22 +50,39 @@ type Model interface {
 	Lock()
 	// Map applies a callback to all elements in this model and returns the
 	// result.
-	Map(callback func(Value) Model) Model
+	Map(callback func(Value) Value) Model
 	// Merge merges data from any Model into this Model.
 	Merge(Model) error
 	// Push a value to the end of the internal data store.
 	Push(value interface{}) error
-	// Reduce iteratively reduces the data set to a single value using a
-	// callback function and returns the result.
-	Reduce(callback func(Value) bool) Value
+	// Reduce iteratively reduces the data to a single value using a callback
+	// function and returns the result.
+	//
+	// The callback function takes two `Value` arguments, the first being the
+	// carry value from the previous iteration (or the first element for the
+	// first iteration) and the second being the current element. The callback
+	// returns a `Value` which becomes the carry value for the next iteration.
+	// After all iterations, Reduce returns the final carry value.
+	//
+	// For a non-empty model, the first element is used as the initial carry,
+	// so the callback is first invoked with that carry and the second
+	// element. For an empty model, Reduce returns nil and does not invoke the
+	// callback.
+	Reduce(callback func(carry, cur Value) Value) Value
 	// Set stores a value in the internal data store. All values must be
 	// identified by key.
 	Set(key interface{}, value interface{}) error
 	// SetData replaces the current data stored in the model with the
 	// provided data.
 	SetData(data interface{}) error
+	// Reverse reverses the order of the data store.
+	Reverse() error
 	// SetID sets this Model's identifier property.
-	SetID(id interface{})
+	//
+	// It returns an error if the model is read-only (for example, after
+	// Lock has been called) or if id is invalid or of an unsupported type
+	// for the implementation.
+	SetID(id interface{}) error
 	// SetType sets the model type. If any data is stored in this model,
 	// this property becomes read-only.
 	SetType(typ ModelType) error
diff --git a/sorter/sorter.go b/sorter/sorter.go
index bc77933..fd98967 100644
--- a/sorter/sorter.go
+++ b/sorter/sorter.go
@@ -1,17 +1,34 @@
 package sorter
 
 // SortFlag provides a type for sort flags
-type SortFlag int
+type SortFlag uint
 
 const (
-	// SortByKey - sort hash data by key
-	SortByKey SortFlag = iota
+	// SortByValue - sort data by value using type-stratified comparison:
+	// nil < bool < numeric < string < other. This is the default/zero value.
+	SortByValue SortFlag = 0
+
+	// SortByKey - sort hash data by key.
+	SortByKey SortFlag = 1 << 0
+
+	// SortAsc - sort data in ascending order. This is the default.
+	SortAsc SortFlag = 1 << 1
+
+	// SortDesc - sort data in descending order.
+	SortDesc SortFlag = 1 << 2
+
+	// SortAsString - when sorting data use string comparison via cast. This is
+	// a tiebreak for SortByValue and the default for SortByKey.
+	SortAsString SortFlag = 1 << 3
+
+	// SortReverse - reverse the order of the data set after sorting.
+	SortReverse SortFlag = 1 << 4
 )
 
 // Sorter describes a sorter.
 type Sorter interface {
 	// Reverse reverses the order of the data set.
-	Reverse(SortFlag) error
+	Reverse() error
 	// Sort sorts the model data.
 	Sort(SortFlag) error
 	// Len returns the number of items stored in this model.