This fixes a bug with elements with multiple class attributes. In this case,
the class attribute in the null namespace would only be considered if it was
the first class attribute in the list.
This fixes a panic if this code was ever called on an element with a class
attribute in a non-null namespace. In this case, the attribute would not have
been parsed into a list of tokens, so value_tokens_forever() would have
returned None.
However, this function is, as far as I can tell, never called, because of the
way selectors are evaluated in layout. ('Return the selectors that match this
node' rather than 'return the nodes that match this selector'; the latter
uses only each_class.)
Extracted out of #5649
* add more hyperlinks to associated specification for structs/methods
* follow redirects and update links
* replace broken links
* removal of WHATWG multipage page name since the page name is not
guaranteed to be stable
Extracted this out of #5649
This commit was created with the following commands:
```
find . -iname "*.webidl" -type f -print0 | xargs -0 sed -i '' 's/http:\(.*\)whatwg.org/https:\1whatwg.org/g'
```
```
find . -iname "*.rs" -type f -print0 | xargs -0 sed -i '' 's/http:\(.*\)whatwg.org/https:\1whatwg.org/g'
```
Extracted this out of #5649
This commit was created with the following commands:
```
find . -iname "*.webidl" -type f -print0 | xargs -0 sed -i '' 's/http:\(.*\)whatwg.org/https:\1whatwg.org/g'
```
```
find . -iname "*.rs" -type f -print0 | xargs -0 sed -i '' 's/http:\(.*\)whatwg.org/https:\1whatwg.org/g'
```
Accidentally fixes bugs about Document::createElementNS() where the
implementation of "validate and extract" used to check whether the local name
extracted from the qualified name was "xmlns" instead of the qualified name
itself.
For the majority of these cases, `as_slice` can be removed due to
`Deref`. In particular, `Deref` for:
* `String` -> `str`
* `Atom` -> `str`
The latter of those two requires, a bump of the locked `string-cache`
library
