The rustdoc reference looks like this:

fn contains(&self, other: Self) -> bool
where
    Self: Sized,

Whether all set bits in a source flags value are also set in a target flags value.

The function takes self and other arguments, but the doc comment defines it in terms of a source and target. It's not specified which argument is the source and which one is the target. Is it source.contains(target) or target.contains(source)?