Template:Evaldemo/3(edit talk links history) shows the call of a template or predefined template and its result, for documentation.

Usage:
{{Evaldemo/3|left side|up to 3 additional parameters}}
{{Evaldemo/3|left side|up to 3 additional parameters|s=separator}}
The default separator is "gives", use s== to get "=". The first parameter has to be specified and can't be empty, compare Template:Evaldemo(edit talk links history). Please note that for colon functions the first parameter belongs to the left side before the "|" vertical bar aka pipe, use {{evaldemo}} for examples without any vertical bar.
Examples:
  1. {{Evaldemo/3|#ifeq: 1.00|+1|okay}}
    {{ #ifeq: 1.00 | +1 | okay }} gives okay
  2. {{Evaldemo/3|#ifeq: this|that | true | false|s=is}}
    {{ #ifeq: this | that | true | false }} is false

Optional substitution with subst=subst: is not supported. It's anyway against the spirit of this demo template showing what another template actually does, and not what it did some time ago.