Reponsive images, sizes

[strarsis]

In many cases the tailor grid is used in a responsive (not just adaptive) layout,
the images are scaled relatively to available width.

A proper sizes attribute would allow the browser to pick the right image file,
speed up page loading considerably because this can already happen during HTML parsing -
also this is the correct usage of srcset.

Ideally tailor would allow adding extra information of its outmost width so
it can calculate correct sizes attributes for the element it contains.

[andrew-worsfold]

@strarsis - Are you able to provide more detail about an approach for adding "extra information" that could be used for this purpose?

[strarsis]

@andrew-worsfold: The theme has to inform about the main content area, ideally for each viewpoint width/height. The tailor elements have to share this available space. When a tailor element got a fluid width (like 1/3 of the available space), the sizes attribute needs to become calc(<available-width> * 0.3).
Similar issue: WordPress/gutenberg#869