Unexpected matches in @capture of function definition

I ran into some unexpected matching behavior in a function definition (see below). I'm not sure if this should be a match or not. However, if it is a match it seems to by swapping xsym and args (e.g., I would expect xsym to get :x rather than args getting that). I'm guessing this can be worked around by using some of the function definition documentation?

julia> @MacroTools.capture(:(function f(x; n=100) return 1 end), function funsym_(xsym_, args__) body_ end)
true

julia> xsym
:($(Expr(:parameters, :(n=100))))

julia> args
1-element Array{Any,1}:
 :x

Start with the @MacroTools.capture entry point and the linked function-definition documentation, then reproduce the Julia example exactly. Compare the bindings assigned to xsym and args with the documented matching semantics; done means the intended behavior is established and the example is corrected or clearly documented.