This documentation is transcluded from Template:Issubst/doc.
This template tests whether a template is being substituted.
Usage
...in a template...
{{issubst}}
...more template...
It will produce "yes" if being substituted and nothing if not being substituted. This allows for something like:
{{ {{{|safesubst:}}}#if: {{issubst}} | text if substituted | text if not substituted }}