Defines a named constant. See the section on constants for more details.
The name of the constant is given by name; the value is given by value.
The optional third parameter case_insensitive is also available. If the value TRUE is given, then the constant will be defined case-insensitive. The default behaviour is case-sensitive; i.e. CONSTANT and Constant represent different values.
Returns TRUE on success or FALSE on failure.
See also defined(), constant() and the section on Constants.