Abstract base class for all 2D physics joints. Abstract base class for all joints in 2D physics. 2D joints bind together two physics bodies ([member node_a] and [member node_b]) and apply a constraint. Returns the joint's internal [RID] from the [PhysicsServer2D]. When [member node_a] and [member node_b] move in different directions the [member bias] controls how fast the joint pulls them back to their original position. The lower the [member bias] the more the two bodies can pull on the joint. When set to [code]0[/code], the default value from [member ProjectSettings.physics/2d/solver/default_constraint_bias] is used. If [code]true[/code], the two bodies bound together do not collide with each other. Path to the first body (A) attached to the joint. The node must inherit [PhysicsBody2D]. Path to the second body (B) attached to the joint. The node must inherit [PhysicsBody2D].