one of the documented procedures in this installation of the ACS
ad_register_styletag   tagname   tag_documentation   proc_body
What it does:
Defines a new site-wide style, includes an ADP tag and a procedure for use by .tcl pages (starting with "ad_style_"). The supplied procedure body should reference $string and $tagset (the variables given in the AOLserver Tcl API docs for ns_register_adptag)
Defined in: /web/philip/tcl/ad-style.tcl

Source code:

    ns_share ad_styletag
    ns_share ad_styletag_source_file
    set generated_proc_name "ad_style_$tagname"
    proc_doc $generated_proc_name  {{string ""} {tagset ""}} "Proc generated by ad_register_styletag to support the $tagname ADP tag." $proc_body
    # let's register the ADP tag now
    ns_register_adptag $tagname "/$tagname" $generated_proc_name
    set ad_styletag($tagname) $tag_documentation
    set ad_styletag_source_file($tagname) [info script]