Original post (http://arch01.forum.helldorado.fr/index.php?topic=1938.msg23614#msg23614) from Geof regarding the definition of a legal target, especially in the context of explosive weapons. Note: the discussion initially came from the question of AndrewGPaul about Chams' aura here (http://arch01.forum.helldorado.fr/index.php?topic=1965.msg22268#msg22268), so it affects the wording of the aura.
Legal target
A legal target for a melee, ranged, explosive, or blast attack is an enemy model which may (as far as special abilities/effects are concerned) be the target of a melee combat, a ranged attack, an explosive attack, or a blast attack.
A friendly model may never be considered as the only legal target for an explosive or blast attack. Therefore it is impossible to place an explosion or a blast template over enemy models that are not legal targets (because of the Discretion special ability for example) even if a friendly model is also under the template.