I'm looking for the type of documentation, were for example if I want to find the page(s) describing the function "XYZ" I can type XYZ into a search field and get a link directly to that page or pages.
I don't want to manually visit every single page and search for XYZ.
We don't have a built-in search feature on the docs. However it is pretty well indexed by google. A search for site:nodered.org XYZ will find what you want.