LINE The current line number of the file.

FILE The full path and filename of the file. If used inside an include, the name of the included file is returned. Since PHP 4.0.2, FILE always contains an absolute path with symlinks resolved whereas in older versions it contained relative path under some circumstances.

DIR The directory of the file. If used inside an include, the directory of the included file is returned. This is equivalent to dirname(FILE). This directory name does not have a trailing slash unless it is the root directory. (Added in PHP 5.3.0.)

FUNCTION The function name. (Added in PHP 4.3.0) As of PHP 5 this constant returns the function name as it was declared (case-sensitive). In PHP 4 its value is always lowercased.

CLASS The class name. (Added in PHP 4.3.0) As of PHP 5 this constant returns the class name as it was declared (case-sensitive). In PHP 4 its value is always lowercased.

METHOD The class method name. (Added in PHP 5.0.0) The method name is returned as it was declared (case-sensitive).

NAMESPACE The name of the current namespace (case-sensitive). This constant is defined in compile-time (Added in PHP 5.3.0).

[http://www.php.net/manual/en/language.constants.predefined.php]