The tv-wikilink-template variable controls the value of the href attribute on the HTML a element generated by the $link widget. The tv-filter-export-link, if defined, it takes precedence over the tv-wikilink-template variable.
The variable is treated as if it was a macro with the following parameters:
uri_encoded parameter but percent-encoded again, i.e. with its % characters further converted to %25\define tv-wikilink-template() ../tiddlers/$uri_encoded$.html
The variable defaults to #$uri_encoded$.
See also the tv-get-export-link variable, which dominates over this one.