15. The sizzle general structure of jquery source parsing. htm

Sizzle is a pure JavaScript implementation of the CSS selector engine, it has a completely independent, no library dependencies, small, easy to extend and good compatibility and so on.
The selectors API specification defines methods Queryselector () and Queryselectorall (), but ie6,7 does not support both methods.
Inside Sizzele, if the browser supports method Queryselectorall (), the method is called to find the element and, if not supported, simulates the behavior of the method.
Sizzle supports almost all CSS3 selectors, and returns results according to the document location.

The above intercept is just a general frame of the Sizzle section, where the specifics of the details are written as far as possible in the later chapters.