List all udev rules (e.g. for a device)?

I want to know how I can list all udev rules.

I know that in they can be potentially stored as lines (one line = one rule) in *.rules files in these directories

/etc/udev/rules.d
/lib/udev/rules.d
/run/udev/rules.d
/var/run/udev/rules.d

Therefore I though I can find all rules by simple concating all the *.rules files in those directories. This seems not to be working (because some rules are executed which I cannot find anyware as rules in these directories).

At best I thought that there is a command to the udevadm interface which will let me print out all the rules that udev currently has.