[css-anchor-position-1] Add CSSOM interfaces

[xiaochengh]

No description provided.

[xiaochengh]

@tabatkins

[tabatkins]

Are we sure we want this rule to be readonly? The @try rule isn't readonly (you can adjust the style), so it feels a little weird for @position-fallback to be.

If it's not readonly, we can probably just inherit from CSSGroupingRule and add the name attribute.

[xiaochengh]

OK, I'll make them mutable (aka I'll make a closer copy of CSSKeyframesRule).

If it's not readonly, we can probably just inherit from CSSGroupingRule and add the name attribute.

I think inheritance from CSSGroupingRule is more appropriate if the child rules can be of any type.

If only one type of child rules are allowed, then it should inherit from CSSRule (again using CSSKeyframesRule as an example).

[tabatkins]

(aka I'll make a closer copy of CSSKeyframesRule).

Nah CSSKeyframesRule has a weird set of operations. This is why I'm suggested CSSGroupingRule instead.

I think inheritance from CSSGroupingRule is more appropriate if the child rules can be of any type.

If only one type of child rules are allowed, then it should inherit from CSSRule (again using CSSKeyframesRule as an example).

Nothing about CSSGroupingRule suggests it's specifically for multiple child rule types. The "insert a rule" operation checks if the rule type is allowed in that context.

If they'd been created in the opposite order, we've have CSSKeyframesRule inherit from CSSGroupingRule rather than use some weird bespoke operations.

[xiaochengh]

Done. Now it's inheritting from CSSGroupingRule.

I guess the only thing remaining is the ASCII art.