Introduced in v5.1.18 The system tag $:/tags/RawMarkupWikified/TopHead marks wikified tiddlers to be included as raw markup at the top of the <head> section in the generated HTML file.
Note that the wiki must be saved and reloaded in order for a raw markup tiddler to take effect. Also note that global macros are not available by default within raw markup tiddlers; you can use the ImportVariablesWidget to explicitly import them.