Minecraft wiki entry for Development_versions, associated text: New attribute: generic.attackReach.
Represents the attack reach of a player.
Only used by players.
Default base: 3.0; minimum: 0.0; maximum: 6.0.
Value is the number of blocks away the player can attack from.
Weapon modifier now modifies generic.attackReach with Operation 0 and UUID 26cb07a3-209d-4110-8e10-1010243614c8.
Added a "Combat Reach" parameter (using attribute generic.combatReach) to swords, hoes and tridents.