I have created a user macro called bgcolor, which the user can use to highlight text. The body of the user macro looks like this:
<font style="BACKGROUND-COLOR:$param0">$body</font>

This works fine in the Wiki Markup editor – I can highlight a specific section of a paragraph using the bgcolor macro.

However, when I transition to the Rich Text editor, all macro opening and closing tags are automatically placed on their own line. Therefore, any internal section of a paragraph which I have highlighted turns into a separate paragraph.