Anchor Points or Fragment Identifiers are used extensively to take users to particular parts of a Webpage.  A classic example of this being a site's FAQs page where you'd have a list of clickable FAQs at the top of the page that, when clicked, take you to the full text of the question and the answer which are either lower down the same page or perhaps are part of another page.

The problem comes when these are coded incorrectly or the page changes and the links no longer reflect what's actually on the target page.

Examples:

1. A clickable FAQ entry points to a Fragment Identifier called Q10 which should be located further down the page but Q10 doesn't exist. 
2. A clickable FAQ entry points to a Fragment Identifier called Q10 but there are TWO (or more) Q10s

These errors will be reported under Code Quality under the Unknownid for the first example and under the Bad value item for the second.  We added them to the Code Quality category as these types of error won't cause a failure in the same way as, say, a broken link would (though there are similarities) they just won't work as you intended them to.  For instance if you click on one of the clickable FAQs in the example and no Q10 Identifier exists the Webpage would remain in exactly the same place.  Or in the case of duplicate Q10 Identifiers the browser will take you to the FIRST instance of Q10 which may or may not be correct.

Fragment Identifiers may also be used by a site's Style Sheets (CSS) or by JavaScript on the site.  Again missing or duplicated Identifiers will cause unpredictable and, therefore, undesirable results.

Some sites will see these new checks impact their Code Quality score when they've made limited unrelated changes.  It's important that we extend the checks we do to identify issues on your websites.  The side effect of this could be that we find you more problems to fix but all of the issues we raise could be impacting the visitors to your site.