Template:Multiple substs

{{subst:subst}}#ifexpr:{{{2}}}>0|{{subst:subst}}multiple substs|{{{1}}}a| }} {{subst:subst}}multiple substs|{{{1}}}b|}}|{{{1}}}}}

Substituting this template produces one or more new substitution template calls, allowing recursive change of a page, see Help:Recursive conversion of wikitext.