[class.member.lookup]/1:

Member name lookup determines the meaning of a name (id-expression) in a class scope (6.3.7). Name lookup can result in an ambiguity, in which case the program is ill-formed. For an id-expression, name lookup begins in the class scope of this; for a qualified-id, name lookup begins in the scope of the nested-name-specifier. Name lookup takes place before access control (6.4, Clause 14).

The highlighted text is confusing as it assumes that an id-expression is not a qualified-id The term id-expression above should be replaced by unqualified-id..

A second point to consider: why is the word ambiguity in italics?