Basics
XUI is available to the entire document as x$. It is a function, that accepts a query selector. The syntax is mostly chainable and should be familiar to anyone who has worked with jQuery.
Quick Example
x$('a.navigation').css({ background:'blue' });
The query selection engine is based on the browser implementation of querySelectorAll so its fast. Real fast. XUI allows for a single expression, an element or an array of elements to be passed
More Examples
x$(window); // The Window
x$(element); // An Existing Element
x$('ul#globalnav li a.selected'); // A CSS3 Selector
x$(['li','div#foo']); // An Array of Selectors
x$('li','.selected','#some_id'); // A comma list of CSS3 Selectors