RE: Surface JavaScript APIs for selector match changes

± var sel = new Selector(".foo", document)
± sel.onchange  = function(event) { } instead.
± 
± ~TJ

FWIW, I like the idea of having a Selector object. Then we can start imagining other useful functions like helpers to compare the relative priority of two selectors, or whether a selector depends on features X or Y.

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Just because the conversation is there, I wanted to mention I made a prollyfill for Selectors Observers in the past, that works in that way:

    querySelectorLive("h2~p", {
        onadded: function(e) {
            console.log("h2~p added:");
            console.log(e.textContent);
        },
        onremoved: function(e) {
            console.log("h2~p removed:");
            console.log(e.textContent);
        }
    });

    https://github.com/FremyCompany/querySelectorLive/

The polyfill is sufficiently good (performance-wise) to be used on real websites while we wait for a standard approach. 

Regarding the idea of sending an array of elements being removed/added, I believe it would be more efficient because much less functions calls need to be done (for loops are cheap), but at the same time it makes the code a bit less elegant, I think.