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This is woefully out of date in almost every aspect
This page was originally created in 2011 and hasn't been updated since. If you need an up to date reference just go to MDN.
https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Selectors
A quick filterable reference for CSS Selectors Level 3 built using isotope.js.
Available at https://dumaurier.github.io/CSS-Selectors-Reference/