Editing Template:If/doc (section)

==Usage==
'''Where p is output for a true statement and q is output for a false statement.'''

*<syntaxhighlight lang="text" inline>{{if||x| p | q }}</syntaxhighlight> gives "{{if||x| p | q }}". Notice the empty first parameter, seen as two adjacent vertical bars.
*<syntaxhighlight lang="text" inline>{{if|expr|2<3| p | q }}</syntaxhighlight> gives " p "
*<syntaxhighlight lang="text" inline>{{if|eq| u |u| p | q }}</syntaxhighlight> gives "{{if|eq| u |u| p | q }}"
*<syntaxhighlight lang="text" inline>{{if|exist| Help:Link | p | q }}</syntaxhighlight> gives "{{if|exist| Help:Link | p | q }}"
*<syntaxhighlight lang="text" inline>{{if|error|{{#expr:x}}| p | q }}</syntaxhighlight> gives "{{if|error|{{#expr:x}}| p | q }}"

Compare:
*<syntaxhighlight lang="text" inline>{{#if:x| p | q }}</syntaxhighlight> gives "{{#if:x| p | q }}"
*<syntaxhighlight lang="text" inline>{{#ifexpr:2<3| p | q }}</syntaxhighlight> gives "{{#ifexpr:2<3| p | q }}"
*<syntaxhighlight lang="text" inline>{{#ifeq: u |u| p | q }}</syntaxhighlight> gives "{{#ifeq: u |u| p | q }}"
*<syntaxhighlight lang="text" inline>{{#ifexist: Help:Link | p | q }}</syntaxhighlight> gives "{{#ifexist: Help:Link | p | q }}"
*<syntaxhighlight lang="text" inline>{{#iferror:{{#expr:x}}| p | q }}</syntaxhighlight> gives "{{#iferror:{{#expr:x}}| p | q }}"

For example, with a template named ''Template:Template name'' containing the code <syntaxhighlight lang="text" inline>{{#ifeq: {{{parameter}}} |u| p | q }}</syntaxhighlight>, entering the code <syntaxhighlight lang="text" inline>{{Template name|parameter=u}}</syntaxhighlight> into an article gives "p", but <syntaxhighlight lang="text" inline>{{Template name|parameter=v}}</syntaxhighlight> gives "q".

The text of either the then-clause or else-clause is only processed and expanded when triggered. Hence, any templates in use are only expanded once the then-clause or else-clause is matched, otherwise they are skipped as merely paired braces, "&#123;&#123;" with "}}".

===Indentation===
If indenting the markup, care must be taken to avoid extra newlines when indenting "}}" on the next line. An extra bar pipe "|" can be added after the else-clause to complete that text, and allow "}}" to then be placed anywhere without adding a newline into the else-clause. For example:
:::* <syntaxhighlight lang="text">{{if|{{{1|}}}
    |then found parameter 1|else no parameter 1| ← extra "|" ends else-clause
}}</syntaxhighlight >
When the else-clause is indented to the next line, a newline (CR/LF) is added:
:::* <syntaxhighlight lang="text">{{if|{{{1|}}}
    |then found parameter 1 ← extra newline here
    |else noparameter 1|
}}</syntaxhighlight>
To indent the else-clause, split an [[HTML]]-form comment, as "<code>&lt;!--</code>" with next line as "<code>--&gt;|else...</code>". Unless each then-clause and else-clause is carefully tested, to watch for extra newlines, then the results are likely to cause broken lines, with extra line breaks for each newline. For that reason, a global edit with simple search-and-replace of "<code>{#if:</code>" to "<code>{if||</code>" is likely to leave newline problems, wherever the original markup was wrapped to indent either the else-clause or "}}" of each if-structure. Indenting the then-clause is not a problem.