Attacks of Opportunity

A character wielding a melee weapon creates a threatened area around them. This area includes all cells the character can reach with this weapon.
Actions of an enemy within this threatened area or one who attempts to leave it may provoke an attack with this melee weapon. Such attacks are called attacks of opportunity.
An attack of opportunity:
:Consists of a single regular attack with the character's currently equipped melee weapon.
:Can be parried or dodged by the target just like with normal attacks.
:Can be enhanced by various talents the attacker might have, including those that specifically affect attacks of opportunity by increasing their damage, hit chance, or other parameters.
:Does not spend the attacker's action points.
A character in a threatened area:
:Cannot use ranged weapons with the exception of pistols and shotguns.
:Will trigger an attack of opportunity if they try to leave the threatened area — in other words, if they move from one of the threatened cells to a non-threatened cell.
:Must spend 3 MP to move between two adjacent threatened cells instead of the usual 1 or 2 MP. Entering a threatened area costs the usual 1 MP.
:Cannot perform certain actions (such as firing most ranged weapons) and provokes attacks of opportunity by performing certain other actions. Some actions can be performed as normal. You can tell what consequences, if any, taking a certain action will have by checking the tooltip that appears when you select a character's ability or weapon.
:Can be threatened by multiple characters at once. When attacks of opportunity are provoked, all characters who threaten the cell make the attacks one after another.