• Writing Adblock Plus filters:
  https://adblockplus.org/en/filters
  Describes older syntax, but all things are still actual for uBlock Origin.

• The same manual, extended version:
  https://help.eyeo.com/en/adblockplus/how-to-write-filters

• uBlock Origin manual:
  https://github.com/gorhill/uBlock/wiki/Procedural-cosmetic-filters
  https://github.com/gorhill/uBlock/wiki/Static-filter-syntax
  https://github.com/gorhill/uBlock/wiki/Inline-script-tag-filtering

• List of uBlock Origin scriptlets:
  https://github.com/gorhill/uBlock/wiki/Resources-Library

• Yet another manual:
  https://github.com/DandelionSprout/adfilt/blob/master/Wiki/SyntaxMeaningsThatAreActuallyHumanReadable.md

• Russian version:
  https://adguard.com/kb/ru/general/ad-filtering/create-own-filters/

• Syntax quirks:
  https://github.com/gorhill/uBlock/wiki/Syntax-quirks
  https://github.com/uBlockOrigin/uBlock-issues/wiki/Filter-performance

Examples:

All elements after ##.wrapper-content-main > h2 (but not text):
##.wrapper-content-main > h2 ~ *
##.wrapper-content-main > h2 + *

Shadow root issue:
https://github.com/uBlockOrigin/uBlock-issues/issues/803

Matches-css with regexps (from gorhill wiki):
facet.wp.pl##div[class^="_"]:matches-css(background-image: /^url("data:image/png;base64,/)

https://github.com/gorhill/uBlock/wiki/Static-filter-syntax#permissions

||example.com$replace=/bad/good/

Some xpath good examples (for :xpath(arg)):
https://devhints.io/xpath