Where to find detailed advanced search syntax documentation

[Maltimore]

In the agenda, I'm trying to get only TODO items matching a certain TODO state (in my case NEXT). You need to use the advanced search syntax for this (nvim-orgmode docs: orgmode-advanced_search). From the documentation it is not clear how to do it. I could however guess from the examples that in order to search for a TODO keyword, I need to add slash in front (so search term is /NEXT). My question is, where is this properly documented? Even the emacs orgmode advanced search site has no explanation of this slash behavior:

https://orgmode.org/worg/org-tutorials/advanced-searching.html

Am I looking in the wrong places?
Edit: It's quite clear from the examples that one needs to use the slash in order to search for TODO keywords, I guess my question is more general: how exactly does this syntax work. Do tags search terms always come before TODO keyword search terms? Or could I do it the other way round? In that case, what is the separator character (the equivalent of slash for tags). How do tag and TODO searches play with categories etc.?