13 Templates [temp]

13.8 Name resolution [temp.res]

13.8.3 Dependent names [temp.dep] Type-dependent expressions [temp.dep.expr]

Except as described below, an expression is type-dependent if any subexpression is type-dependent.
this is type-dependent if the current class ([expr.prim.this]) is dependent ([temp.dep.type]).
An id-expression is type-dependent if it is a template-id that is not a concept-id and is dependent; or if its terminal name is or if it names a dependent member of the current instantiation that is a static data member of type “array of unknown bound of T” for some T ([temp.static]).
Expressions of the following forms are type-dependent only if the type specified by the type-id, simple-type-specifier, typename-specifier, or new-type-id is dependent, even if any subexpression is type-dependent:
Expressions of the following forms are never type-dependent (because the type of the expression cannot be dependent):
sizeof unary-expression
sizeof ( type-id )
sizeof ... ( identifier )
alignof ( type-id )
typeid ( expression )
typeid ( type-id )
:: delete cast-expression
:: delete [ ] cast-expression
throw assignment-expression
noexcept ( expression )
[Note 1: 
For the standard library macro offsetof, see [support.types].
— end note]
A class member access expression is type-dependent if the terminal name of its id-expression, if any, is dependent or the expression refers to a member of the current instantiation and the type of the referenced member is dependent.
[Note 2: 
In an expression of the form x.y or xp->y the type of the expression is usually the type of the member y of the class of x (or the class pointed to by xp).
However, if x or xp refers to a dependent type that is not the current instantiation, the type of y is always dependent.
— end note]
A braced-init-list is type-dependent if any element is type-dependent or is a pack expansion.
A fold-expression is type-dependent.
A pack-index-expression is type-dependent if its id-expression is type-dependent.