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I've just started code according to VIP WordPress Coding Standards and I stuck with sanitization. I know that all outputs need sanitization without any exception. But how can I do sanitization of a function which has HTML code output itself? Eg. function yoast_breadcrumb() from Yoast's WordPress SEO plugin which outputs HTML formatted breadcumb..?

<?php echo yoast_breadcrumb( '', '', false ); ?>

Output:

<span prefix="v: http://rdf.data-vocabulary.org/#"><span typeof="v:Breadcrumb"><a href="https://rnc-wordpress-wrongware.c9.io" rel="v:url" property="v:title">Main Page</a></span> › <span typeof="v:Breadcrumb"><span class="breadcrumb_last" property="v:title">Page doesn't exist</span></span></span>
  • You don't. yoast_breadcrumb() is already sanitizing by itself. – TheDeadMedic Mar 9 '15 at 10:58
  • I know that it's. But please read VIP WP standards, you have to sanitize everything. Here is good explanation - vip.wordpress.com/2014/06/20/… – Emetrop Mar 9 '15 at 11:02
  • Check out wp_kses() for sanitizing HTML. – TheDeadMedic Mar 9 '15 at 11:04
  • So do I need every single function check for output, find out which html tags are used and write them all to the wp_kses function ok? It's so much work. – Emetrop Mar 9 '15 at 11:12
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    Agreed, but unlikely. There is no shortcut or win-win. If you want to strictly adhere to VIP coding standards, you need to put the work in - and accept there will always (potentially) be a consequence of aggressive sanitization. – TheDeadMedic Mar 9 '15 at 11:23
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The more elaborate data is, the harder it is to both formulate and implement sanitization process.

For a number this might be as simple as "integer" and (int)$number.

For HTML this is highly not trivial with different possibilities of desired scope (no HTML tags? some blacklisted tags? some whitelisted tags? what about embedded scripts? CSS?) and very challenging implementation.

While WP does have wp_kses() implementing sanitization of HTML, it's relatively slow and its reputation is less than stellar (or so I read in context of other established sanitization libraries).

I would say that in question as stated, the practical expectation is that function engineered to act as template tag is expected to produce sanitized output.

If you don't believe it to, it would probably make more sense to audit it (and report any discovered shortcomings to developer) rather than try to sanitize complex output.

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