Reactions are code objects that run when a message is fired - essentially a message handler attached to an instance of data.

Reactions can be defined only for messages that have a definition (a MsgDef instance). Some data definitions inherit MsgReactionsPreset and can have reactions (message handlers) attached to any of their instances. Ractions can also have a target which can filter out messages.

Message definitions (or MsgDef) are presets which describe a message or event. Their Id must match the message or event they describe, as well as their Params. Finally the message or event can be associated with a specific Target they are concerned with.

Message reaction presets (or MsgReactionPreset) are presets that contain code which can react to messages being fired, similar to global message handlers (see OnMsg). This message handler is associated with the preset instance and it's lifecycle. When the reaction function is called, the first parameter is always preset.

This type of data can contain event handlers that are attached to units (their Target is Unit), while the preset is associated with the unit in some way. Instead of reacting to global Lua messages, these handlers react to events the units can fire themselves by calling self:CallReactions(event_id, ...). When the reaction function is called, the first two parameters are always preset, unit.

Note that Unit inherits ReactionObject.

function ReactionObject:AddReactions(instance, list, insert_locations) : Registers all handlers from the reaction objects in list. These reactions are associated with the object instance.

function ReactionObject:RemoveReactions(instance) : Removes the reactions associated with the object instance.

function ReactionObject:AddEventReaction(event_id, instance, handler) : Registers a single event handler (as opposed to a Reaction object). The handler will react to the event event_id.

function ReactionObject:RemoveEventReactions(event_id, instance) : Removes all event handlers associated with this event_id and instance.

ReactionObject:CallReactions(event_id, ...) : Emits an event, which will call all registered reactions/handlers.

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