API to handle polygons with holes

Hello,

The paper is a bit unclear, but the Algorithm 1 cited there holds only for actual rings, not whole polygons by their definition.
To have proper support for holes one would need to calculate the parity for each hole and aggregate that

Namely we would only need to do something along the lines of:

function inpolyholes(p, rings...; in::T=1, on::T=-1, out::T=0) where {T}

    outerring = first(rings)
    innerrings = Base.tail(rings)

    res = inpolygon(p, outerring; in, on, out)

    isempty(innerrings) && return res

    k = 0
    res == in && (k += 1)

    for ring in innerrings
        ringres = inpolygon(p, ring; in, on, out)
        if ringres == on && (ringres != in && ringres != out) # to properly handle the case where on is equal to either in or out.
            return on
        end

        ringres == in && ( k += 1 )
    end

    iszero(k % 2) && return out
    return in
end

Start by reading the existing inpolygon API and the cited Algorithm 1, then trace how rings are currently represented and tested. Add a polygon-with-holes entry point that aggregates the outer ring and inner-ring results by parity, including the stated boundary-value behavior; done means points inside, outside, and on holes return the expected values.