How does .livequery() work when it only receives one parameter? -

i visiting https://github.com/brandonaaron/livequery trying find syntax of .livequery(). can see there in official documentation, .livequery() can receive 2 or 3 parameters:

// selector: selector match against // matchedfn: function execute when new element added dom matches $(...).livequery( selector, matchedfn );  // selector: selector match against // matchedfn: function execute when new element added dom matches // unmatchedfn: function execute when matched element removed dom $(...).livequery( selector, matchedfn, unmatchfn ); 

however, in source code examining, see .livequery() receiving 1 parameter. example:

$('.js-truncate').livequery(function() {     .................................. }); 

from understand , based on see in official documentation, first parameter of .livequery() "selector". mean when .livequery() receives single parameter, parameter in case?: function(){.......}. thank you.