12 Overloading [over]

12.2 Overload resolution [over.match]

12.2.2 Candidate functions and argument lists [over.match.funcs] Initialization by constructor [over.match.ctor]

When objects of class type are direct-initialized, copy-initialized from an expression of the same or a derived class type ([dcl.init]), or default-initialized, overload resolution selects the constructor.
For direct-initialization or default-initialization that is not in the context of copy-initialization, the candidate functions are all the constructors of the class of the object being initialized.
For copy-initialization (including default initialization in the context of copy-initialization), the candidate functions are all the converting constructors ([class.conv.ctor]) of that class.
The argument list is the expression-list or assignment-expression of the initializer.