New for CMake 3.22, !6222 adds a new `PKG_CONFIG_ARGN` variable for the `FindPkgConfig` module. The docs contain both conflicting and misleading information about this new variable. The start of the docs list `PKG_CONFIG_ARGN` as one of the variables that the module sets. This is only half true, as it is set as a cache variable, so after it has been set once, it won't be changed by the module. Furthermore, being a cache variable, it can be modified by the user. The variable is mentioned again in the _Variables Affecting Behavior_ section, this time as a variable that the user may set. These two sections seem to be in conflict -- the first portrays it as a variable the module sets, the latter section paints it as a variable intended for the user to set. Looking at the implementation, it seems that the intention is that this is a user-modifiable variable, but it is initialised from the `PKG_CONFIG` environment variable. The first section should be updated to make the way the `PKG_CONFIG_EXECUTABLE` and `PKG_CONFIG_ARGN` variables are set and intended to be used clearer.