php.net
PHP Manual
Function signatures and the comments that still save afternoons.
MDN Web Docs
mdn.dev / CSS / flex
Maintained by Mozilla with help from the web. Pages for every CSS property, DOM interface and HTTP header you will actually search at 23:00. Examples are short. Browser-compat tables sit at the bottom so you do not guess.
Wire listed it under Docs because it is the default second tab after a search, not a tutorial that goes stale in a year.
JavaScriptHTMLCSS
Also in Docs
caniuse.com
Can I use
Browser support tables. Green enough, or wait another year.