I don't know what YW means, Triplane.

To digress for a moment here, though, another Montgomery-related folk tune used in hymnals is the French carol whose usual French first line goes "Les anges dans nos campagnes". This tune is generally called IRIS in British hymnals, because it first gained hymnic currency as the tune for Montgomery's "Angels from the realms of glory". In the USA that hymn is almost always sung to REGENT SQUARE, while a variant of IRIS usually called GLORIA or GLORIA (Barnes) [for the arranger, Edward Shippen Barnes] is used for English versions of the French Christmas carol, most commonly "Angels we have heard on high", less commonly Woodward's "Shepherds, in the field abiding", apparently a translation of a Latin text, Quem vidistis, pastores, used in the matins service on Christmas Day. Whether the French is also a translation of the matins responsory I don't know. In his interesting Christmas carol collection Joy of Christmas, former UK prime minister Edward Heath sets another text, beginning "When the crimson sun had set", to GLORIA.

FWIW