Use xsd:key/xsd:keyref instead of xsd:id/xsd:idref?

[shorowit]

Currently HPXML uses xsd:id and xsd:idref, which allows an idref to point to any id in the HPXML file, even if it makes no sense. This means that every software tool must do some error-checking.

From what I've read, xsd:key and xsd:keyref are supposed to provide all the same capabilities as xsd:id and xsd:idref while allowing much more flexibility -- like defining constraints on what element type(s) can be referenced.