Remember that the @var rule will match the contents of variables literally, vs. running them as a rule:
>> var: [some rule]
== [some rule]
>> parse [[some rule] [some rule]] [some @var]
== [some rule]
You can evaluate an expression to literally match, too:
>> parse [[some rule] [some rule]] [some @(reverse copy [rule some])]
== [some rule]
Now there's a powerful new twist: You can match in a spliced fashion, using an isotopic block!
>> var: [some rule]
>> parse [some rule some rule] [some @(spread var)]
== ~[some rule]~ ; isotope
And you can synthesize a product that may be a splice or not!!!
>> append [a b c] parse [1 2 3] [block! | spread across some integer!]
== [a b c 1 2 3]
>> append [a b c] parse [[x y z]] [block! | spread across some integer!]
== [a b c [x y z]]
Encoding the splicing intent on the value is clearly the way to go. Seems obvious now, but hindsight is 20/20.