Invalid subtype relation with `xml`

[KavinduZoysa]

trafficstars

Description: $subject

type X xml;
type XE xml<xml:Element>;
type XP xml<xml:ProcessingInstruction>;
type XC xml<xml:Comment>;
type UX XE|XP|XC|xml:Text;

In the current implementation, X is identified as a subtype of UX which is not correct.