So this question turns on how our plugin will recognize what is or is not a galley file that it controls.  The Label is automatically created from a file suffix of galley file.  But since user can change label, looking at this field alone could have our plugin miss it.  

First to say I avoided having our plugin create its html galley file as the native HTML Galley class object, so I recall when I was testing the isHTMLGalley() it didn't return true.  I was just trying to avoid the situation where a user clicks on an HTML galley that our plugin had created, and got presented with the form for uploading css and images.

I was also trying to avoid the situation where the plugin was taking control of any galley that had .html in its file suffix since editors may have uploaded other html files or have past articles with prepared html galleys.

I considered the idea that our plugin creates its own label for items it controls, but that wouldn't make the article link area look that pretty.  

A practical solution would I suppose be to just read the html and see if it was generated by the document markup server, and if so, then do the rewrite.  Ok?