Editing Help/Templates (section)

=== Default values === <!--T:56-->
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If you transclude a template that expects parameters, but do not provide their arguments, in this way:
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 <translate><!--T:58--> <nowiki></nowiki></translate>

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in the numbered parameters example above you would get the following:
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Since no arguments were passed in, the template presents the parameters themselves, instead of their respective values. In these cases, it may be useful to define ''default'' values for the parameters, i.e. values that will be used if no value is passed in. For example, if the template contents are changed to:
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<syntaxhighlight lang=moin>
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'''A little thank you...'''
for }.
Hugs, }</translate>
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then <code><nowiki>}</nowiki></code> defines that if no argument is provided for parameter <code>}</code>, then the value <code>everything</code> will be used. Similarly, <code><nowiki>}</nowiki></code>, defaults parameter <code>}</code> to value <code>Me</code>. Now, transcluding the template again without passing any argument results in the following:
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<!-- strictly speaking, this example is false, because the template call was changed to obtain the desired effect - but the effect is the same if the template is defined as described -->
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</nowiki></code></tvar> or <tvar name=2><code><nowiki></nowiki></code></tvar>, the <tvar name=5><code>foo</code></tvar> template considers the <tvar name=3><code>bar</code></tvar> parameter to be <tvar name=4><code>""</code></tvar>.</translate> <translate><!--T:233--> This is different from omitting the parameter altogether, which leaves it undefined and triggers the default value mechanism described above.</translate>
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{{note|1=<translate><!--T:342--> If you need to treat an empty string the same way as a missing parameter, you can use a conditional operator through an extension like [[<tvar name=1>Special:MyLanguage/Extension:ParserFunctions</tvar>|ParserFunctions]].</translate> <translate><!--T:343--> For instance, <tvar name=1><code><nowiki>}|}|undefined}}</nowiki></code></tvar> returns undefined if the parameter is either undefined or empty, while <tvar name=2><code><nowiki>}</nowiki></code></tvar> does so only if the parameter is undefined.</translate>
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<translate><!--T:194--> Default values are often used to specify alternate names of parameters.</translate>
<translate><!--T:195--> For example, if you have <tvar name=1><code><nowiki>} }}}</nowiki></code></tvar>, the template will first look for a parameter named "<tvar name=2>a</tvar>".</translate>
<translate><!--T:196--> If it is not set, it will use the parameter named "<tvar name=1>b</tvar>".</translate>
<translate><!--T:197--> If neither "<tvar name=1>a</tvar>" nor "<tvar name=2>b</tvar>" is set, it will output nothing.</translate>

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