I want to add a button to tinyMCE editor on new post page. With this toturial I managed to get the button work perfectly, but there is something I couldn't figure out. When you insert a "More" tag, an image will appended to the html with appropriate 'background-image'. See screenshot bellow:

But when you switch to 'Text' mode there is a html comment like this: <!--more-->.

I could add the image in the html but on 'Text' mode there is an img tag.


I want to have something like this: <!--my-custom-tag-->
How wordpress manage to do this? Or how could I append a custom tag on tinyMCE editor?