About This HTML Issue
The rel attribute on an <a> element has the value noindex, which is not a recognized link type. The validator matched it against the registered keywords and guessed it might be a misspelling of index.
In practice noindex is rarely a typo for index. Authors usually write rel="noindex" because they want to keep a page out of search results, but rel cannot do that. The attribute describes the relationship between the current document and the linked resource, not whether a page should be indexed.
Indexing is a page-level directive. To keep a page out of search results, add a robots meta tag to that page's <head>, or send the equivalent X-Robots-Tag HTTP header. Both apply to the page being excluded, not to a link pointing at it.
If your goal is to stop search engines from passing ranking through a link, the correct rel value is nofollow.
Invalid example
<a href="/private" rel="noindex">Members area</a>
Valid example
Use rel="nofollow" on the link when you want search engines to ignore it:
<a href="/private" rel="nofollow">Members area</a>
To keep the destination page itself out of search results, control indexing on that page instead:
<meta name="robots" content="noindex">
Find issues like this automatically
Rocket Validator scans thousands of pages in seconds, detecting HTML issues across your entire site.