Set attribute based on value of another - attribute_filter enhancement?

[OJFord]

Sorry if this is already possible, but I don't think it is: I'd like to be able to use attribute_filter, or something like it, in order to set a different attrB using (or not) the value from the attrA that was present and found by the filter (attrB may or may not exist already).

For example it might look something like:

use ammonia::Builder;
let a = Builder::new()
    .attribute_filter(|element, attribute, value| {
        match (element, attribute) {
            ("a", "href") => Some(hashset![("href", value), ("title", value)]),
            _ => None
        }
    })