If left empty (default), the URL is derived from the global MantisBT path ($g_path, see
Section 5.3, “Path”), replacing the URL's path component by the wiki engine string (i.e. if $g_path = 'http://example.com/mantis/' and $g_wiki_engine = 'dokuwiki', the wiki URL will be 'http://example.com/dokuwiki/').