Wait, I'm confused. I was under the impression that we decided that the CTR instrument v1 should be simple and for a single element (first one returned by document.querySelector), so if a developer needed to attach a CTR instrument to every element in a collection, they had to do it explicitly – not provide a collection of elements to the CTR instrument to keep track off. And that a single element case was not a collection-of-length-1, but the only case the instrument handles.

I think if you wanted to make it easier for developers to accomplish the task, perhaps a wrapper that replicates this pattern

$( 'a.ext-campaignevents-events-list-link' ).each( function( index, element ) {
    ClickThroughRateInstrument.start(
        'a.ext-campaignevents-events-list-link:nth-of-type(' + (index + 1) + ')',
        'Collaboration list event link'
    );
} );

In T395144#10853364, @mpopov wrote:

Wait, I'm confused. I was under the impression that we decided that the CTR instrument v1 should be simple and for a single element (first one returned by document.querySelector), so if a developer needed to attach a CTR instrument to every element in a collection, they had to do it explicitly – not provide a collection of elements to the CTR instrument to keep track off.

You're right. I had gotten myself in a muddle about ClickThroughRateInstrument.start() and .stop(). That said, I think having a ClickThroughRateInstrument.startMany() method would:

1. Keep the logic around "What does it mean to start an instrument" within the implementation of the instrument
2. Provide a good name for what's going on
3. Help folks keep their code DRY

I like it!