Changing `normal` to `running`

[svgeesus]

running: the image animation plays, without synchronization with any other instance of the same image on the page.

If the value is changed from normal to running, does it:

• keep running from where it was, but now with no guarantee of future synchronization
• start running from the start of the animation

Originally posted by @svgeesus in #1615

[svgeesus]

This issue was raised before the document was adopted as a CSS ED and refers to wording which has now changed. The current wording is:

running
Like normal, the animation of animated images is run normally, as determined by the image format and the host language,

However, animation timelines are scoped per element: among the content image and decorative images of a single element, any animated images with the same absolute URL, the same image data, and with an image-animation computed value of running must be rendered synchronized to the same timeline as a group, distinct from the timeline of images in other elements, with the timeline starting at the time of the least recent addition to the group.

The original question still stands, however.

[bramus]

Maybe the synchronization part needs a separate control? Something like a image-animation-clock prop to indicate whether the clock is synchronized or not.