Clarify which elements can be tracked by elementtiming

[JamesIves]

Firstly, just wanted to say that this addon is awesome. Thank you for putting it together!

It would be great if the documentation clarified which elements can be tracked with the elementtiming attribute. Took me a while to realize that custom elements cannot be tracked with it.

It also seems like it cannot recognize elements that are slotted within the shadow root of a custom element, for example if I had a component called my-image that has an img component in its shadowroot with elementtiming="image" applied, the addon completely ignores it. It will only work if the img element is slotted within the light DOM of another component with the attribute applied.

[mattcosta7]

@JamesIves yes! This is definitely something we could improve docs on! element-timing has a few interesting edges!

Would you be open to submitting an improvement?

The element-timing spec has details on which elements are timing-eligible

An element is timing-eligible if it is one of the following:
an img element.
an image element inside an svg element.
a video element with a poster frame.
an element with a contentful background-image.
a text node.

I'm hopeful that container-timing can replace/augment this once it has better support!

[JamesIves]

Absolutely! I'll throw something together

[JamesIves]

Put together a PR here: #80

[mattcosta7]

closed via #80

Thanks!