Question

I was just looking at the jQueryUI button plug-in and noticed this

$("button, input:submit, a", ".demo").button();

I never seen something like this. Is this like multiple selects in one jQuery selector?

Answer 1

The second argument (".demo" in your example) is the context, basically your selector is restricted to match only descendants of a determined context:

$(expr, context)

Is just equivalent to use the find method:

$(context).find(expr)

Give a look to the documentation of the jQuery function:

Selector Context

By default, selectors perform their
searches within the DOM starting at
the document root. However, an
alternate context can be given for the
search by using the optional second
parameter to the $() function. For
example, if within a callback function
we wish to do a search for an element,
we can restrict that search:

$('div.foo').click(function() {
  $('span', this).addClass('bar');
  // it will find span elements that are
  // descendants of the clicked element (this)
});

Also notice that the selector you post "button, input:submit, a", is called Multiple Selector, and there you can specify any number of selectors to combine into a single result, just by separating them by a comma.