Just what I was looking for

If you regularly need to use the standard Text Editor, use WP-Editor plugin instead.

HTML is a new area for me. I have dabbled over the years but have only recently had to do any heavyweight work in it.

I Just started using collapse-o-matic plugin to create help pages with collapsing sections. The problem I had was that while you can build your content in the Visual Editor you HAVE to finalise your content in HTML to remove spurious formatting put there by the Visual Editor.

The standard text editor is really hard to use for that purpose. So I looked for a text editor that used line numbering to make it easier to follow the text. And then I found WP-Editor which provided line numbers and so much more. Syntax highlighting – WOW