I think XHL it is the reactance between High voltage to Low voltage windings-what usually we call it "transformer reactance" X12, if there are only 2 windings,
and will be XHL,XHT and XTL if there are 3 windings. This is the notation proposed by IEEE in
Distribution System Analytical Data Dictionary
Transformer impedance includes also transformer resistance.In order to find the transformer reactance one has to know the
resistance or at least the ratio R/X