When you add content, visual studio shows it as an error in the xml editor and says it can't contain content. However if you ignore that it builds find and the content is visible in the control.
When you add content to what? Please post an example of what you're talking about.
Sorry, I was in a rush when I added this and left out some details.
I'm editing a bundle theme in visual studio 2010 with wix 3.7 installed. If I change the line in the rtftheme to contain text like so:
<Editbox Name="FolderEditbox" X="11" Y="143" Width="-91" Height="21" TabStop="yes" FontId="3" FileSystemAutoComplete="yes">[InstallFolder]</Editbox>
I get a squiggly line under the "[InstallFolder]" text, and a warning:
"The element cannot contain text. Content model is empty.
This works perfectly fine in the bundle, the edit box has the install path in it, so I expect it's just an issue with the xml schema (which in my file is http://wixtoolset.org/schemas/thmutil/2010).