When I wrote the An+B parser, it was guaranteed to have no
non-whitespace tokens after it. This is no longer true with the `of
foo` syntax, so this patch corrects the logic when there is no `+B`
segment.
This makes this case shown on Twitter work correctly. :^)
https://twitter.com/simevidas/status/1506657566012678151
`text-shadow` does not support this, so this way we can still use the
same parsing code.
It's OK that we still assign a ShadowPlacement value to the
ShadowStyleValue, since it will just get ignored when painting
text-shadows, but if it appears in the property value then that is a
syntax error.
The `text-shadow` property is almost identical to `box-shadow`:
> Values are interpreted as for box-shadow [CSS-BACKGROUNDS-3].
> (But note that the inset keyword are not allowed.)
So, let's use the same data structures and parsing code for both. :^)
There's really no reason to use doubles here, except at the time I
wanted to use doubles everywhere in CSS. I now realize that is
excessive, so everything can be floats instead.
There was no real benefit to creating the SimpleSelector early and then
modifying it, and doing so made this code harder to follow than it
needs to be.
The spec says:
> <delim-token> has a value composed of a single code point.
So using StringView is a bit overkill.
This also allows us to use switch statements in the future.
This doesn't have parsing support for multiple languages in the same
selector. Support for language subcodes is not great either. But it
does do the basics.
In Selectors level 4, `:nth-child()` and `:nth-last-child()` can both
optionally take a selector-list argument. This selector-list acts as a
filter, so that only elements matching the list are counted. For
example, this means that the following are equivalent:
```css
:nth-child(2n+1 of p) {}
p:nth-of-type(2n+1) {}
```
`<forgiving-selector-list>` and `<forgiving-relative-selector-list>` are
the same as regular selector-lists, except that an invalid selector
does not make the whole list invalid. The former is used by the `:is()`
pseudo-class.
For example:
```css
/* This entire selector-list is invalid */
.foo, .bar, !?invalid { }
/* This is valid, but the "!?invalid" selector is removed */
:is(.foo, .bar, !?invalid) { }
```
Also as part of this, I've removed the `parse_a_selector(TokenStream)`
and `parse_a_relative_selector(TokenStream)` methods as they don't add
anything useful.
This resolves the ambiguity between whether a single number is a number
or a ratio. :^)
Also removed the "no more tokens" checks from
deea129b8c - that logic was completely
wrong, since there are always tokens after a value in the `(123 < foo <
456)` syntax.
As noted, the Parser can't handle the `<number>` syntax for this - it
gets parsed instead by the `<number>` branch. We can't actually resolve
the ambiguity without making the Parser aware of what type each
media-feature is, but I will get to that soon. :^)
For now, we only understand `none`, `normal`, `<image>` and `<string>`.
The various other functions and identifiers can be added later.
We can *almost* use a StyleValueList for this, except it's divided into
two parts - the content, and the optional "alt text". So, I've added a
new StyleValue for it.
This is the only dimension type besides `<length>` that is used in any
media queries in levels 4 or 5 right now. Others can be included
if/when they're needed.
