Make.LangSet of whitespace characters. A sequence of zero or more whitespace characters is stripped off after each token.
Usually the set of whitespace characters is " \t\n\r" i.e. blanks, tabs, newline and carriage return are whitespace characters.
multiline_start, multiline_end, nested
Optional definition of a multiline comment.
Precondition: The start and end of a multiline comment must not be empty.
Optional start of a line comment. The comment spans to the end of the line.
Precondition: The start of a line comment must not be empty.