Function length_logical_px 

pub fn length_logical_px(
    filter: &str,
    param: &str,
    len: Length,
) -> Result<f32, String>

A Length filter param’s logical-px value. Only Px has a fixed logical size here — percent/viewport units have no basis for a filter param — so any other unit is rejected with a message naming it, instead of silently resolving to 0.0. Bare wire numbers decode as Px and stay accepted.

pub because #[react_filter]-generated pack/outset/resolve code calls it from consumer crates (blur shares it in-crate).