In a template that must be substituted, add the following code at the top:

{{ {{#ifeq:{{<includeonly>subst:</includeonly>void}}|{{void}}|void|Error:must be substituted}}| template name }}

Example: en:Template:Demo of template that must be substituted (links, bearbeiten).

while {{subst:Demo of template that must be substituted}} gives "Template body".

See also

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