Validation error "Bad value apple-touch-icon-precomposed for attribute rel on element link: Keyword apple-touch-icon-precomposed is not registered."

Question

I'm getting this error in w3C HTML 5 validator

Line 9, Column 101: Bad value apple-touch-icon-precomposed for attribute rel on element link: Keyword apple-touch-icon-precomposed is not registered. …-icon-precomposed" sizes="72x72" href="images/sl/touch/m/apple-touch-icon.png"> Syntax of link type valid for : A whitespace-separated list of link types listed as allowed on in the HTML specification or listed as an allowed on on the Microformats wiki

How to fix this error?

Answer 1

Ignore it.

If that's the only error you have, then your document is valid HTML5.

Here's what the official (in development) spec states about the <meta> tag: Extensions to the predefined set of metadata names may be registered. I can't find the area in the spec that talks about the "ref" tag values, but the validator treats them similarly (one for links, one for strings), and points us to the extension Wiki. You 'may' register them, but don't have to. In RFC terminology this is a SHOULD not a MUST.

The spec doesn't seem to mandate a fixed list, or use of the Wiki. Doing so would seem odd, as these fields have often evolved with time. It does state that Conformance checkers must use the information given on the WHATWG Wiki MetaExtensions page to establish if a value is allowed or not: values defined in this specification or marked as "proposed" or "ratified" must be accepted. which is an interesting line as it is a specification for the HTML Validators, not HTML5 itself, and doesn't itself make the markup invalid.

In fact, many of these "extensions" are already in the wiki (including your one), they just haven't been accepted. Same with many meta tags, even very common ones. It seems many won't be accepted either.

I think it's very nice of the W3C to create a standardised list of these. It helps developers know what they should be using now and in the future (and can hopefully clean up some things linke reducing the number of ways you can specify a creation date from 5+ to 1).

Unfortunately we are dealing with third parties here (e.g. Apple) – and unless you want to contact every third party who has created one of these informal specification, and tell them to formalize a spec, and submit it to the W3C's list (which may or may not get accepted) what are you to do? At the end of the day you still need to support it.

Anyway, isn't the very point of having these HTML elements to support extensions so vendors don't break the spec by adding new elements to do what the need?

Answer 2

If you move the touch icons into your web root and follow the Apple documentation for naming conventions, you won't actually need to insert the link tags in your HTML and will avoid those validation errors.

The iOS devices will look for the icons in the web root automatically, using the predefined naming conventions and the correct resolution as also outline here. Good luck.