How do you replace text using python qscintilla editor widget?

[enjoysmath]

Here is a broken MWE. It replaces \nat with NN when it starts up, but when you type text it starts entering the text backwards.

Was wondering if there was a recipe for replacing text that replaces only the substring and not the whole document.

import sys
from PyQt5.QtWidgets import *
from PyQt5.QtCore import *
from PyQt5.QtGui import *
from PyQt5.Qsci import *
import re

NAT = re.compile(r"\\nat")

class MyLexer(QsciLexerCustom):
   def __init__(self, parent):
      super(MyLexer, self).__init__(parent)

   def language(self):
      return "SimpleLanguage"

   def description(self, style):
      return ""

   def styleText(self, start, end):
      self.startStyling(start)
      editor = self.parent()
      text = editor.text()[start:end]
      text = NAT.sub('NN', text)
      
      editor.SendScintilla(editor.SCI_SETTEXT, text.encode('utf-8'))
         
myCodeSample = r"""
\nat
""".replace("\n","\r\n")

class CustomMainWindow(QMainWindow):
   def __init__(self):
      super(CustomMainWindow, self).__init__()

      self.setGeometry(300, 300, 800, 400)
      self.setWindowTitle("QScintilla Test")
      self.__frm = QFrame(self)
      self.__frm.setStyleSheet("QWidget { background-color: #ffeaeaea }")
      self.__lyt = QVBoxLayout()
      self.__frm.setLayout(self.__lyt)
      self.setCentralWidget(self.__frm)
      self.__editor = QsciScintilla()
      self.__editor.setText(myCodeSample)     # 'myCodeSample' is a string containing some C-code
      self.__editor.setLexer(None)            # We install lexer later
      self.__editor.setUtf8(True)             # Set encoding to UTF-8
      self.__lexer = MyLexer(self.__editor)
      self.__editor.setLexer(self.__lexer)
      self.__lyt.addWidget(self.__editor)
      self.show()
   def __btn_action(self):
      print("Hello World!")

if __name__ == '__main__':
   app = QApplication(sys.argv)
   QApplication.setStyle(QStyleFactory.create('Fusion'))
   myGUI = CustomMainWindow()
   sys.exit(app.exec_())

Have you solved this problem before? If so, please let me have the recipe :)

[enjoysmath]

def styleText(self, start, end):
   self.startStyling(start)
   editor = self.parent()
   #text = editor.text()[start:end]
   editor.findFirst(NAT.pattern, True, False, False, True)
   editor.replace('NN')

I figured it out by RTFM here: https://www.riverbankcomputing.com/static/Docs/QScintilla/classQsciScintilla.html

It does search the whole document, but I don't care since it's written in C++.