A *subscripting operator function*
is a function named operator[]
that is a non-static member function with exactly one parameter.

For an expression of the form

postfix-expression [ expr-or-braced-init-list ]the operator function is selected by overload resolution ([over.match.oper]).

If a member function is selected,
the expression is interpreted as

postfix-expression . operator [] ( expr-or-braced-init-list )