class_docstr: Represents a match of a variable in the grammar.
  
  :param varname: (string) Name of the variable.
  :param value: (string) Value of this variable.
  :param slice: (start, stop) tuple, indicating the position of this variable
                in the input string.
code: def __init__(self, varname, value, slice):
      self.varname = varname
      self.value = value
      self.slice = slice
  
      self.start = self.slice[0]
      self.stop = self.slice[1]
  
imports: from __future__ import unicode_literals
  import re
  from six.moves import range
  from .regex_parser import Any, Sequence, Regex, Variable, Repeat, Lookahead
  from .regex_parser import parse_regex, tokenize_regex
label_desc: Use image node_id 1 to create a new MatchVariable object from inherited base classes: object with example: obj = MatchVariable(varname, value, slice)