— typedef: vector<music_details> music::mdvector;

This type defines the storage vector that records the expressions to be matched and is also used to obtain the results.

— typedef: vector<music_details>::iterator music::iterator;
— typedef: vector<music_details>::const_iterator music::const_iterator;

This type defines a general iterator that can be used to iterate through the stored expressions.

— typedef: vector<music_details>::size_type music::size_type;

This type defines the type of variable returned from the size() function.