Help:Parameter default
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Note: Information on this page relates to MediaWiki versions 1.6 and later.
This page is currently inactive and is retained for historical reference. Although some of it may still be relevant, this page describes techniques made obsolete by ParserFunctions and Lua. |
Notation: on this page the wikitext {{{A}}}
is written as [a].
In a template, [a|b]
is equal to [a] if that is defined, and else equal to b.
These results [a] and b can be end results, but they can also be parameter names, parameter values, template names, parts thereof, etc.
If the results are template names as part of template calls involving a parameter of the outer template which may be undefined, one can arrange that an inner template is called with a parameter depending on an undefined outer parameter only if the parameter concerned is not actually used in the inner template, e.g. dummy template Template:x0 containing "<noinclude>{{documentation}}</noinclude>
" can be called as {{x0|[a]}}
even if [a] is undefined, see e.g. m:Template:foreach/pass1 (backlinks edit).