Reference documentation for FetchContent

I’ve stumbled upon this code snippet:

FetchContent_Declare(
    box2d
    GIT_REPOSITORY https://github.com/erincatto/box2d.git
    GIT_TAG 7b273b12409252d247b89940d29a8aab0386f570
    GIT_SHALLOW TRUE
    GIT_PROGRESS TRUE
)

and I would like to look up the documentation for GIT_SHALLOW and GIT_PROGRESS. The FetchContent documentation doesn’t cover those. Where can I find a complete reference documentation with an explanantion for all possible values in FetchContent_Declare?

As specified in FetchContent_Declare() documentation, you have to refer to ExternalProject_Add() command documentation for these options.