"apple-touch-icon-precomposed" is not a real value for the rel attribute?

Question

Why do people (h5bp, Mathias Bynens) say to use a <link rel="apple-touch-icon-precomposed"> element? Apple's documentation on this makes no mention of apple-touch-icon-precomposed as a value for the rel attribute.

Apple's docs say this about precomposed icons:

Safari on iOS 7 doesn’t add effects to icons. Older versions of Safari will not add effects for icon files named with the -precomposed.png suffix.

So it seems that we could reference the precomposed apple touch icon like this, right?:

<link rel="apple-touch-icon" href="apple-touch-icon-precomposed.png">

Holliehollifield

In the old (pre-iOS 7) days, precomposed meant that you didn't want iOS to add the icon gloss to your icon, either because you "precomposed" the icon with the gloss, or you don't want the gloss flat out. – Coprolalia

Answer 1

This direct quote from the write-up on touch icons you linked to explains it:

As of iOS 7, no special effects are applied to touch icons anymore, so if you only care about iOS 7 and up you don’t have to use precomposed anymore.

In other words, it’s recommended for optimal display of your touch icons on older iOS versions. Feel free to not use it.

Radiology

I get the fact that IOS7 doesn't add special effects to icons, so if you don't mind older IOS versions not adding effects either, you can rename apple-touch-icon-precomposed.png to apple-touch-icon.png. My question was why people ever used apple-touch-icon-precomposed as a value for the rel attribute. Apple's documentation never mentioned that as a value. Here's an older 2011 version of that doc. – Holliehollifield

“so if you don't mind older IOS versions not adding effects either, you can rename apple-touch-icon-precomposed.png to apple-touch-icon.png” → This doesn’t make sense. Omitting -precomposed means that older iOS versions will add the effects. – Radiology

People used rel=apple-touch-icon-precomposed rather than rel=apple-touch-icon because it had the same effect as making an image available at /apple-touch-icon-precomposed.png rather than /apple-touch-icon.png. – Radiology

Answer 2

My own testing of iOS 6 on an iPad 3 made it seem as though the rel value was necessary when the filename used wasn't apple-touch-icon-*.

Adding -precomposed to an irregular filename (e.g. app-icon76x76.png) had no effect, whereas adding rel="apple-touch-icon-precomposed" removed the effects as expected.

Divestiture