This commit begins to implement the track processing model. When the
`src` attribute is updated, we now fetch the given source file.
Currently, we always fire an `error` event once fetching is completed,
as we don't support processing the fetched data.
This matches the behavior of other browsers, which always set the dirty
checkedness flag when setting checkedness, except when setting the
`checked` content attribute.
In conformance with the requirements of the spec PR at
https://github.com/whatwg/html/pull/9546, this change adds support for
the “switch” attribute for type=checkbox “input” elements — which is
shipping in Safari (since Safari 17.4). This change also implements
support for exposing it to AT users with role=switch.
Currently, the following JS snippet will hang indefinitely:
new DOMParser().parseFromString("<object>", "text/html");
Because the document into which the object is inserted is not active. So
the task queued to run the representation steps will never run.
This patch implements the spec steps to rerun the representation steps
when the active state changes, and avoid the hang when the object is
created in an inactive document.
