hmm, still need to update property_database.js...

Most files are related to test update. The files in testing/web-platform/meta/css/vendor-imports/mozilla/mozilla-central-reftests/* will be dropped after dbraon's sync (from Part 1). Basically, only need to check servo/*. (Other files could be verified by try.)

Hmm, so this is a bit complicated and position parsing was a bit nasty already... What do you think of the following?

Adding the following bits:

impl<S> PositionComponent<S> {
    fn component_count(&self) -> usize {
        match *self {
            PositionComponent::Length(..) |
            PositionComponent::Center => 1,
            PositionComponent::Side(_, ref lp) => {
                if lp.is_some() { 2 } else { 1 }
            }
        }
    }
}

impl Position {
    fn is_three_value_syntax(&self) -> bool {
        self.horizontal.component_count() != self.vertical.component_count()
        // or maybe self.horizontal.component_count() + self.vertical.component_count() == 3
    }
}

Rename the current implementation of parse_quirky to parse_three_value_quirky.

Make Position::parse do something like:

let position = Self::parse_three_value_quirky(..)?;
if position.is_three_value_syntax() {
    return Err(..);
}
Ok(position)

I think that'd be simpler over all. It feels a bit weird that we detect three-value syntax sometimes before, sometimes after, otherwise.

That's ok with me. Using the count of the values to check it is one of my options while working on this, but I'm not sure which way is better. For readability, it's reasonable to address your idea. Thanks.

I forgot to update the parser of background shorthand [1]. Will update it by using parse_three_value_quirky().

[1] https://searchfox.org/mozilla-central/rev/40ef22080910c2e2c27d9e2120642376b1d8b8b2/servo/components/style/properties/shorthands/background.mako.rs#67