Editing WoW:API UnitCastingInfo (section)

=== Returns ===
:;spell: String - The name of the spell, or nil if no spell is being cast.
:;rank: String - The string describing the rank of the spell, e.g. "Rank 1".
:;displayName: String - The name to be displayed.
:;icon: String - The texture path associated with the spell.
:;startTime: Number - Specifies when casting has begun, in milliseconds.
:;endTime: Number - Specifies when casting will end, in milliseconds.
:;isTradeSkill: Boolean - Specifies if the cast is a tradeskill
:;castID: Number - Counts the spellcast(s) since the game has loaded.(added either in or just before 3.2)
:;interrupt: (added in 3.2) Boolean - Returns true if the unit's current cast can not be interrupted by abilities such as Counterspell or Kick. Otherwise, returns false if the cast is interruptible or nil if the unit is not casting. If tested on a Paladin with Divine Shield active, interrupt returns true while the Paladin is casting. Without Divine Shield active, interrupt would return false.)