What kind of "effects" does Safari add to apple-touch-icon?

I've been seeing a lot of websites saying that you can dis开发者_运维技巧able the effects Safari puts on a apple-touch-icon by adding "-precomposed" to the end.

What "effects" exactly does Safari add to the icon?

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Gloss and a drop shadow are added when "-precomposed" is not appended to the tag.