[wp-trac] [WordPress Trac] #34678: Responsive Images: Check if content images already have a sizes attribute

[WordPress Trac]

#34678: Responsive Images: Check if content images already have a sizes attribute
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 Reporter:  jaspermdegroot  |       Owner:  joemcgill
     Type:  defect (bug)    |      Status:  reopened
 Priority:  normal          |   Milestone:  4.4
Component:  Media           |     Version:  trunk
 Severity:  normal          |  Resolution:
 Keywords:  has-patch       |     Focuses:
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Comment (by jaspermdegroot):

 @azaozz

 First of all, I wouldn't recommend inserting the `sizes` attribute in the
 image markup in the post editor, but there might be situations where it is
 the best (least worst) solution. The limitation of the filter is that you
 don't know anything about the context. So if a specific layout is used
 somewhere which warrants a custom `sizes` value, you can only use the
 filter if the combination of image ID/URL and size is unique for that
 situation.

 Having a `sizes` attribute without a `srcset` attribute is indeed useless.
 That would be bad HTML, but not broken/invalid as far as I understood from
 the specs. Only a `srcset` attribute with `w` descriptors and no `sizes`
 attribute is invalid. However, when users add a custom `sizes` attribute
 they know of course that their final markup will also contain the `srcset`
 and I suppose what matters is if the final markup is good or not.

 > Alternatively we can check for the presence of sizes and srcset, and if
 either is present can skip generating both for that image.

 That would be better than not checking at all, to prevent two `sizes`
 attributes in the final markup. Otherwise we would have to document
 somewhere that you are not allowed to add that attribute.

 This would make it more difficult though to add a simple custom `sizes`
 attribute since you would also have to manually create the `srcset`
 attribute. So I think we should decide if there are good use cases for
 inserting a custom `sizes` attribute in the image markup instead of using
 the filter, and if so, I suggest we don't make that harder by requiring a
 `srcset` as well.

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Ticket URL: <https://core.trac.wordpress.org/ticket/34678#comment:11>
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