Type Alias MaskReference 

pub type MaskReference<'a> = NoneOr<Image<'a>>;

https://drafts.csswg.org/css-masking-1/#typedef-mask-reference

<mask-reference> = none | <image> | <mask-source>
<mask-source> = <url>

Since <image> already includes <url>, this simplifies to none | <image>.

Aliased Type

pub enum MaskReference<'a> {
    None(Ident),
    Some(Image<'a>),
}

Variants

None(Ident)

Some(Image<'a>)