Mathematica: HOWTO: Strip an option from an OptionsPattern[] sequence before passing down (propagating) to a function with fewer options

When working with complex hierarchies of functions, sometimes the Options available to a sub-function are not as broad as those of a "parent" (higher) calling function. If you just pass down an OptionsPattern[] that is a superset of the relevant options you'll get a warning. The following shows how to strip off irrelevant options before calling down:

CASE: Strip a single option from an OptionsPattern[] Sequence:

stripOpt::usage = "stripOpt[optName, OptionsPattern[]] 
Strips the Rule identified by 'optName' and returns a Sequence.;

stripOpt[optName_, opts:OptionsPattern[]] :=  Module[
  { map },

  If[ opts =!= Null,
    (
      map = KeyDrop[<|opts|>, optName];
      Sequence[ # -> map[#]& /@ Keys[map] ]
    ),
   (* Must be 3rd argument to If *)
    Sequence[]
  ]
];

CASE: Strip multiple options Rules from an OptionsPattern[] Sequence:

stripOpts::usage = "stripOpts[optName1, optName2,..., OptionsPattern[]] 
Strips all Rules identified by 'optName1', 'optName2', etc. and returns a Sequence";

stripOpts[optNames__,  opts:OptionsPattern[]] := Module[
  { map },

  If[opts =!= Null,
    (
      map = KeyDrop[<|opts|>, {optNames}];
      Sequence[ # -> map[#]& /@ Keys[map] ]
    ),
    (* Must be 3rd argument to If *)
    Sequence[]
  ]
];

One could perhaps uses something more elegant but the above works fine.

Note that if no OptionsPattern[] is provided it returns an "empty" Sequence[] which splices directly in.

Usage example

Options[fChild] = { doThat->False };

fChild[arg_,OptionsPattern[]] := ...

Options[fParent] = { doThis->True, doThat->False };

fParent[arg_, opts:OptionsPattern[] ] := Module[

  fChild[arg, stripOpt[doThis, opts] ]; (* Only passes valid child options *)

  If[OptionValue[doThis], ...]; (* Could be before or after call to child *)
  ...
];

fParent[arg]

fParent[arg, doThis->False]

fParent[arg, doThat->True]

fParent[arg, doThis->False, doThat->True]