Please forgive me if this is a stupid question or has been addressed before. I have searched and can't find an answer.

When customizing the Category "Header" field can I use a Template Global code or can a regular <%include navbar.txt%> code be used or is the header field for html code only? See this post/thread for more information about what I've been trying to do: Subject: Re: Header Customization

Thanks in advance.
Nadine