The "default" tags can be seen at the top of the HTML_Templates.pm file, in the %GLOBALS hash.
In the Category template, you also have access to all the field names in the category table <%field_name%>, and in the Links.html and Detailed.html templates you have access to all the field names in the Links table <%field_name%>
You also have access to any tags specifically passed to the template (check the HTML_Templates.pm file for the tags that are passed in each subroutine. You'll find them in the call to &load_template in each subroutine.
All the dynamc forms search.cgi, add.cgi, etc use the %in hash, so any tags that are passed in your form are available to the script and thus passed to the next level of template via the $in reference.
You can add tags to be passed to all templates that use HTML_Templates.pm by adding them to the %GLOBALS hash.
Remember -- if you call &load_template directly, as is done in some routines, you bypass the %GLOBALS hash, and you have to pass those tags explicitly.
http://www.postcards.com FAQ:
http://www.postcards.com/FAQ/LinkSQL/