No DSL knowledge required, at all. Just shell knowledge, and the willingness to look at sourced shell scripts.
Ouch... Shell (or Bourne Shell to be exact), not bash.
Bash is a type of Shell and it's not* even available (thank goodness) on either of the BSDs in their base system (only as a port and/or package).
On OpenBSD, the actual command line interpreter is actually Korn, not the Bourne, Shell.
And "look at the source" is a sad answer, no matter if the source is a shell script or C program.
The point is that with your example you need domain knowledge, knowing bash is not enough: what does the pexp assignment do, what rc_reload=NO means, should flags be specified in the daemon variable or that's meant to only contain the binary, does that path be full or it takes in consideration a standard PATH?
And now you got two things to know: the bash (or even strictly posix sh) language (which, admittedly, isn't the best one in the world) and the domain specific functions/variables.
This isn't much different than with systemd: the language is much more simple and far less surprising being INI-like (the same as .desktop files), and it's basically just setting a list of rather well documented variables.