This sample constructs an HTMLInfo that acts as a re-implementation of the default text editor.
The implementation is contained in the file TextEditor.js
    and exposes window.TextEditor,
    which is used in this file as the value of myDiagram.toolManager.textEditingTool.defaultTextEditor.
  
This also adds a text validation predicate, okName, as the TextBlock.textValidation property.
    That predicate makes sure that the new string has at least three characters and contains a vowel.
  
You can see additional custom text editors in the Custom TextEditingTool sample.