Is it possible to use multiple variables instead of selectors in jQuery

Just use the add method:

$header_elements.add($footer_elements).css({color:'#ff0000'});

Given a jQuery object that represents a set of DOM elements, the .add() method constructs a new jQuery object from the union of those elements and the ones passed into the method. The argument to .add() can be pretty much anything that $() accepts, including a jQuery selector expression, references to DOM elements, or an HTML snippet.

I found the solutions a few minutes after posting this. For those who are wondering, here it is:

$.merge($header_elements, $footer_elements).css({color:"#ff0000"});

Is it faster? I don't know yet, I'll need to run some tests to find out.

EDIT:

I tested it with JS Fiddle here : http://jsfiddle.net/bgLfz/1/

I tested using selector each time, variable for both selector, variables with $.merge() and using .add(). Each test was run 1000 times.

Results on my side are as follow (from faster to slower):

1. Using $.merge() (average of 7ms)
2. Using both variable one after the other (average of 10ms but the code needs to be duplicated)
3. Using .add() (average of 16ms)
4. Using selectors each time (average of 295ms)