Variable description
Stores the current lexer instance.

Class description
An object for tokenizing parser input. It has the following slots:
textthe lines being parsed; an array of strings
linethe line number being parsed; unlike most indices this is 1-based for friendlier error reporting and integration with text editors
columnthe current column position, zero-based

Custom lexing can be implemented by delegating a tuple to an instance of this class and implementing the skip-word and skip-blank generic words.