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| <title>Conditional Nesting (GNU Texinfo 6.8dev)</title> |
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| <p> |
| Previous: <a href="Testing-for-Texinfo-Commands.html" accesskey="p" rel="prev">Testing for Texinfo Commands: <code class="code">@ifcommanddefined</code>, <code class="code">@ifcommandnotdefined</code></a>, Up: <a href="Conditionals.html" accesskey="u" rel="up">Conditionally Visible Text</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Command-and-Variable-Index.html" title="Index" rel="index">Index</a>]</p> |
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| <h3 class="section" id="Conditional-Nesting-1">15.7 Conditional Nesting</h3> |
| <a class="index-entry-id" id="index-Conditionals_002c-nested"></a> |
| <a class="index-entry-id" id="index-Nesting-conditionals"></a> |
| |
| <p>Conditionals can be nested; however, the details are a little tricky. |
| The difficulty comes with failing conditionals, such as |
| <code class="code">@ifhtml</code> when HTML is not being produced, where the included |
| text is to be ignored. However, it is not to be <em class="emph">completely</em> |
| ignored, since it is useful to have one <code class="code">@ifset</code> inside another, |
| for example—that is a way to include text only if two conditions are |
| met. Here’s an example: |
| </p> |
| <div class="example"> |
| <pre class="example-preformatted">@ifset somevar |
| @ifset anothervar |
| Both somevar and anothervar are set. |
| @end ifset |
| @ifclear anothervar |
| Somevar is set, anothervar is not. |
| @end ifclear |
| @end ifset |
| </pre></div> |
| |
| <p>Technically, Texinfo requires that for a failing conditional, the |
| ignored text must be properly nested with respect to that failing |
| conditional. Unfortunately, it’s not always feasible to check that |
| <em class="emph">all</em> conditionals are properly nested, because then the |
| processors could have to fully interpret the ignored text, which |
| defeats the purpose of the command. Here’s an example illustrating |
| these rules: |
| </p> |
| <div class="example"> |
| <pre class="example-preformatted">@ifset a |
| @ifset b |
| @ifclear ok - ok, ignored |
| @end junky - ok, ignored |
| @end ifset |
| @c WRONG - missing @end ifset. |
| </pre></div> |
| |
| <p>Finally, as mentioned above, all conditional commands must be on lines |
| by themselves, with no text (even spaces) before or after. Otherwise, |
| the processors cannot reliably determine which commands to consider |
| for nesting purposes. |
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