First thing to notice is that the default font is sans serif.
Make it fixed width like Courier New.

If you resize to small your resize code generates an error
VB Code:
  1. Private Sub Form_Resize()

  2.     'Resize the txtDocument editing window to fit the form

  3.     txtDocument.Width = frmMain.ScaleWidth - 4

  4.     txtDocument.Height = frmMain.ScaleHeight - 4

  5. End Sub
The -4 creates a negative Height and Width
I think I have a resize module somewhere.
I'll try and dig it out.

For some reason the horizontal scroll bar is not working on the text box.
If you hold down a key you cant tell whether it has wordwrapped or if it is a new word.

An insert HTML outline would be good too.
HTML Code:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
        "http://www.w3.org/TR/html4/loose.dtd">
<HTML>
   <HEAD>
      <TITLE>HTML 4.01 Transitional</TITLE>
	<META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=UTF-8">
   </HEAD>
   <BODY>
      
   </BODY>
</HTML>
ConTEXT has a lot of useful features like this.
It might be worth downloading it and picking out the best bits.
One feature that is has is the autocomplete is based on external text files.
This is useful as the user can add/modify/extend it as he wishes.