Adding modifier to dimensions

I'm not a super experienced Onshape user, but I'm looking into its ISO GPS capabilities when it comes to drawings (in particular ISO 14405-1:2025). The geometric tolerances and datums seem to be very well implemented, but I'm struggling with adding modifiers to dimensions of features of size, such as envelope, GX, GN, LP, etc. Is there something I'm overlooking or is this not implemented? Ideally you'd have control of the modifiers of both the upper and lower limits of size. I guess it's not really a thing in ASME where the envelope principle is rule #1, but it's not default for us ISO folk…