Before diving deeply into how the selector works, let’s look at how the web page is structured, see some basic syntax examples, and explore the SQL analogy.
Fundamentally, it comes back to CSS selectors identifying page elements. Sizzle.js is the engine that powers the jQuery library, and it extends the number of selectors available to provide more granular access to elements on the page. jQuery extends this further by traversing the tree that represents the web page, and visiting and acting upon a set of specified elements.