[expr.prim.pack.index]/1 A nested id-expression in the pack-index-expression need not denote a pack

[BlowingWind314]

[expr.prim.pack.index]/1 says

pack-index-expression:
id-expression ... [ constant-expression ]

The id-expression P in a pack-index-expression shall be an identifier that denotes a pack.

id-expressions within the constant-expression need not denote some packs.

The id-expression P in of a pack-index-expression shall be an identifier that denotes a pack.