Fires when the player's shapeshift form changes. Unlike other shapeshift-related events, this function refers specifically to shapeshifting -- therefore including some abilities which are not presented via the stance/shapeshift bar and excluding some which are. For example, applies to shaman Ghost Wolf form, druid shapeshifts, and some quest-related shapeshifting, but not warrior stances, paladin auras, or rogue stealth. This does fire for Death Knight presences, however.