Link Resource Timing entry

[npm1]

Currently, the Element Timing API exposes only two of the attributes from Resource Timing: responseEnd and name. For images, it seems useful to instead provide a direct link to the Resource Timing entry corresponding to the element. For text, we will not be able to provide this at first, and in fact text elements may not correspond to any Resource Timing entry. But overall it seems useful to provide a pointer to RT from ET.

This issue is filed based on the discussion at w3c/user-timing#17.

[sergeychernyshev]

Text might enjoy a link to a custom font resource used to render it.

[npm1]

Correct! I mention that we might not be able to provide this at first because on our text proposal we do not wait until webfonts have loaded. In the future, we could, but text is also a bit trickier because a single block of text (like a paragraph) could be using multiple webfonts (so we'd need an array of RT entries).

[sergeychernyshev]

Agreed. Just wanted to weigh in as I see that being important quite often and requires some attention when we use User Timing for this.

Good point about multiple web fonts - not sure how this will handle font-display: swap situation though... we currently measure it anyway knowing that there is a difference in experience between browsers that support it and browsers that don't. Same applies to other values, I assume.