class_docstr: Matches documents containing a given phrase.
code: def replace(self, fieldname, oldtext, newtext):
      q = copy.copy(self)
      if q.fieldname == fieldname:
          for i, word in enumerate(q.words):
              if word == oldtext:
                  q.words[i] = newtext
      return q
  
imports: from __future__ import division
  import copy
  from whoosh import matching
  from whoosh.analysis import Token
  from whoosh.compat import u
  from whoosh.query import qcore, terms, compound
label_desc: Use image node_id 10 for calling the Phrase obj's underlying member method code with example usage: obj.replace(fieldname, oldtext, newtext) and returns: q