Template:Meta/Help/Substitution

For issues involving the substitution of templates, such as how to control whether subtemplates are substituted as well when the parent template is substituted, see Help:Substitution.
The template {{Trim}} can be used to strip any initial or final whitespace from unnamed parameter values if this would cause problems; named parameter values are automatically stripped in this way.
For debugging templates, the following techniques are sometimes helpful:
Use subst: to substitute a template (rather than transcluding it), which can show more clearly what is happening when the template is transcluded; see Help:Substitution.
Use msgnw: (short for "message, nowiki") to more-or-less transclude the wikitext of the template page rather than the processed contents. It is not perfect: lists are rendered, comments are removed, and single newlines are replaced with spaces (which is particularly confounding when transcluding wikitext tables).
Use Special:ExpandTemplates to see the full recursive expansion of one or more templates.