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

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


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.