I was basically using Confluence as an HTML editor for some emails that I was drafting. I noticed that once I saved the Confluence page all of my 'style' tags were changed to 'mce_style' tags. For instance:

<br style:"line-height=15px;"> was changed to <br mce_style:"line-height=15px;">

See Screenshot 1.

I also noticed that the 'mce_' style tag is added to <a href> tags. In fact, the link is duplicated. For instance Confluence TinyMCE editor renders these links as:

<a href="http://www.atlassian.com" mce_href="http://www.atlassian.com">Atlassian</a>

See Screenshot 2

This is unfortunate because I wanted to copy the HTML from the Confluence page and paste elsewhere. I will now have to remove all of the 'mce_' style tags.

Also, Confluence's editor changes all lower-case tags to upper-case tags. For instance, <br> = <BR>