While the DPH Guidance has it's controversial parts (Rec IX), the guidance on interpreting "directly participating in hostilities" is quite authoritative.
And that should be emphasized: the Geneva Conventions allow the targeting of military objectives, combatants (i.e. members of armed forces) and "civilians directly participating in hostilities". The Guidance just interprets the latter and arguably widens the scope, because - without the invention of "continuous combatant function" - you could attack e.g. members of Hamas' armed wing during an attack and in preparation of one. Now you can attack them at any time.
And that should be emphasized: the Geneva Conventions allow the targeting of military objectives, combatants (i.e. members of armed forces) and "civilians directly participating in hostilities". The Guidance just interprets the latter and arguably widens the scope, because - without the invention of "continuous combatant function" - you could attack e.g. members of Hamas' armed wing during an attack and in preparation of one. Now you can attack them at any time.