Demo for producing a substitution demo. In this case it shows the result of substituting Template:Tsd for a particular parameter value. After a change in that template it just requires pressing edit and save on the page Template:Tsubst tsdd to update the substitution demo produced by transcluding this template.

"{{tsubst tsdd|abc}}" gives "{{subst:tsd|abc}} gives "{{subst:tsubst tsd|start - abc - end|abc}}"." [1]

This template Template:Tsubst tsdd uses Template:Tsubst tsd. Thus for every template like Template:Tsd two auxiliary templates are needed for producing substitution demos.