[jQuery] Does $('input#myId') search for inputs first or is it optimised?

[Remy Sharp]

I should really know this, but I've come to realise I'm not 100% sure.

Does this:

$('input#myId')

...search for all inputs first then narrow down to the ID, or does
jQuery work out before hand that "there can be only one" Id - and
therefore is the same, with respect to processing to:

$('#myId')

Cheers.

Remy.