Annex C (informative) Compatibility [diff]

C.1 C++ and ISO C++ 2020 [diff.cpp20]

C.1.3 [expr]: expressions [diff.cpp20.expr]

Affected subclause: [expr.sub]
Change: Change the meaning of comma in subscript expressions.

Rationale: Enable repurposing a deprecated syntax to support multidimensional indexing.

Effect on original feature: Valid C++ 2020 code that uses a comma expression within a subscript expression may fail to compile.
For example: arr[1, 2] // was equivalent to arr[(1, 2)], // now equivalent to arr.operator[](1, 2) or ill-formed