docstr: Return the start of the innermost open expression or None
code: def open_expression_start(self):
      """Return the start of the innermost open expression or None"""
      if self.__in_brackets:
          return self.__bracket_start
      elif self.__group_depth:
          return self.__group_starts[-1]
  
imports: import re
  import wx
  import wx.stc
label_desc: Use image node_id 14 for calling the RegexpState obj's underlying member method code with example usage: obj.open_expression_start() and returns: self, self