code: def _markproduction(self, prod, tree=None):
      if tree is None:
          tree = self._tree
      for i in range(len(tree.subtrees()) - len(prod.rhs())):
          if tree["color", i] == "white":
              self._markproduction  # FIXME: Is this necessary at all?
  
          for j, node in enumerate(prod.rhs()):
              widget = tree.subtrees()[i + j]
              if (
                  isinstance(node, Nonterminal)
                  and isinstance(widget, TreeSegmentWidget)
                  and node.symbol == widget.label().text()
              ):
                  pass  # matching nonterminal
              elif (
                  isinstance(node, str)
                  and isinstance(widget, TextWidget)
                  and node == widget.text()
              ):
                  pass  # matching nonterminal
              else:
                  break
          else:
              # Everything matched!
              print("MATCH AT", i)
  
imports: import re
  from tkinter import Button, Canvas, Entry, Frame, IntVar, Label, Scrollbar, Text, Tk, Toplevel
  from nltk.draw.tree import TreeSegmentWidget, tree_to_treesegment
  from nltk.draw.util import CanvasFrame, ColorizedList, ShowText, SymbolWidget, TextWidget
  from nltk.grammar import CFG, Nonterminal, _read_cfg_production, nonterminals
  from nltk.tree import Tree
label_desc: Use image node_id 10 for calling the CFGDemo obj's underlying member method code with example usage: obj._markproduction(prod, tree) without return types