Semicolon in attribute value?

Hello.

Does anyone know how to get a semicolon to validate in an attribute value? I have a ton of content that has elements tagged with the following revisionflag attributes:

revisionflag="html;htmlcond"
revisionflag="pdf;pdfcond"


I think our transforms look for these values to see which image to use in an output, and the transforms work fine. The problem is that I get a ton of validation errors in my editor for all of these entries and they create a lot of noise that could drown out a real error. Is there a way for me to make these semicolons work? For example, can I escape them in the DTD so that the validator thinks that they are allowable values?

Or, is there a way for me to tell the validator to ignore these errors (I think this might be more difficult).

Here is a snippet from my dbpoolx.mod file:

<!ENTITY % revisionflag.attrib
            "revisionflag    (changed
                                    |added
                                    |deleted
                                    |off
                                    |pdf
                                    |pdfcond
                                    |html
                                    |htmlcond
                                    |kindle
                                    |kindlecond
                                    |kindle-epub-cond)                  #IMPLIED">

I tried adding the semicolon values, but that breaks the DTD. I tried using single and double quotes around them and that also broke the DTD. I cannot change the way that the attribute values are displayed in the book XML (although that would obviously be the easiest way to do this) because I am in a multi-author environment. I need this to be a change I can make to the DTD so that it will work with all of our existing content and just get rid of my validation errors.

Thanks!

Eric N.