Meta template that returns "yes" if evaluated during substitution, and the empty string if evaluated during transclusion.
Note that this template must be used in safesubst mode to work properly:

{{ {{{|safesubst:}}}issubst}}
  • "{{issubst}}" → ""
  • "{{subst:issubst}}" → "yes"
  • {{Require subst}}: Prints an error unless substituted.
    • {{Subst check top}}{{Subst check bottom}}: Same purpose, but used as a pair.
    • {{Subst only}}: For the doc of the above templates; prints a message asking for it be substituted.
    • {{Nosubst}}: The reverse of {{Subst only}}. For the doc of templates which should not be substituted; prints a message asking for it not to be substituted.
  • {{Issubst}}: Returns "yes" if substituted.
  • {{Ifsubst}}: Forks if substituted or not.