what part(s) of jQ UI do I need for addClass()?

what part(s) of jQ UI do I need for addClass()?

quick question.... what part(s) of jQ UI do you need to download to use this feature?

https://jqueryui.com/addClass/

every feature it should say what part(s) of jQ UI you need to download, minimum.... I downloaded jQ UI core, but it's not working....  with jQ UI, I always like to download no more than necessary...;-)
(also, it should say what's earliest version of jQ core you need for it...  I'm using 1.11.3, (what I was able to find here) it's not working...)

thank you....