Represent reference actually to some constant that was defined
before.
It could be constant that was introduced via "define",
could be reference to class constant : Clazz::CONST.
It could be function name ( defined by user or php function ).
The methods below are mutually exclusive.
Represent super interface as mark for
source element that can be identifiers.
Method name ( when method is called ) can be not
just identifier but it can be also changed
to variable.
This is entry point for semantic access of PHP content.
Model consist from set of management methods and
information retrieval methods.
This class is immutable for given Document ( it doesn't
mutate when something changed in source ).