Simplify <image> element content model

[jarek-foksa]

I'm not sure what is the purpose of allowing the following elements as children of <image>: <image>, <use>, <iframe>, <video>, <audio>, <foreignObject>.

Are they supposed to be shown as a fallback content when the image fails to load? If yes, then this behavior should be documented, otherwise I would remove them from the content model.

[AmeliaBR]

This refers to "structurally external elements" being listed in the allowed content model of image.

I suspect that's an error. I can see no reason for it.

Anyone else have any knowledge of this?

[jarek-foksa]

<marker> also doesn't make much sense as a child of <image>. Unlike e.g. <clipPath> or <mask>, you can't set a marker on an image.

[prlbr]

I can imagine an <audio> description of an image being useful in some contexts as fallback for visually impaired users. But I don’t know whether this is done in practice by anyone and whether user agents support this in a sensible way.

[jarek-foksa]

I would also remove "paint server elements" from the content model because images are not paintable.

To sum this up, I would redefine the content model of <image> to allow only "animation elements", "descriptive elements", <clipPath>, <mask>, <script> and maybe <style> (depending on whether issue #162 gets resolved).

[jarek-foksa]

@nikosandronikos what is the reason for leaving the <marker> element in the content model? As far as I know markers can't be applied on <image> elements.

[nikosandronikos]

@jarek-foksa Sorry, that was just a mistake on my part. Fixed now. Thanks for reviewing