The editing command that relies the most on this, `insertLinebreak`,
did not perform a layout update after inserting a `<br>` which caused
this algorithm to always return false. But instead of actually building
the layout tree needlessly, we can check the DOM tree instead.
The spec calls for a couple of very specific whitespace padding
techniques whenever we canonicalize whitespace during the execution of
editing commands, but it seems that other browsers have a simpler
strategy - let's adopt theirs!
We previously had PropertyOwningCSSStyleDeclaration and
ResolvedCSSStyleDeclaration, representing the current style properties
and resolved style respectively. Both of these were the
CSSStyleDeclaration type in the CSSOM. (We also had
ElementInlineCSSStyleDeclaration but I removed that in a previous
commit.)
In the meantime, the spec has changed so that these should now be a new
CSSStyleProperties type in the CSSOM. Also, we need to subclass
CSSStyleDeclaration for things like CSSFontFaceRule's list of
descriptors, which means it wouldn't hold style properties.
So, this commit does the fairly messy work of combining these two types
into a new CSSStyleProperties class. A lot of what previously was done
as separate methods in the two classes, now follows the spec steps of
"if the readonly flag is set, do X" instead, which is hopefully easier
to follow too.
There is still some functionality in CSSStyleDeclaration that belongs in
CSSStyleProperties, but I'll do that next. To avoid a huge diff for
"CSSStyleDeclaration-all-supported-properties-and-default-values.txt"
both here and in the following commit, we don't apply the (currently
empty) CSSStyleProperties prototype yet.
The spec doesn't say they should exist, so we should not
`VERIFY_NOT_REACHED()` when they don't. Prevents a crash in the WPT
`editing/event.html` tests.
The algorithm referenced to in the Editing spec whenever they talk about
obtaining the "resolved" style or value is actually implemented in
ResolvedCSSStyleDeclaration, so use that instead of going directly to
the computed styles.
The DOM spec defines what it means for an element to be an "editing
host", and the Editing spec does the same for the "editable" concept.
Replace our `Node::is_editable()` implementation with these
spec-compliant algorithms.
An editing host is an element that has the properties to make its
contents effectively editable. Editable elements are descendants of an
editing host. Concepts like the inheritable contenteditable attribute
are propagated through the editable algorithm.
In all these cases there should be an ancestor available, but it
definitely cannot hurt to be a bit more defensive about this and prevent
nullptr dereferences.
To facilitate the implementation of "delete" and all associated
algorithms, split off this piece of `Document` into a separate
directory.
This sets up the infrastructure for arbitrary commands to be supported.
