A node that may modify Skeleton3D's bone with associating the two bones. Base class of [SkeletonModifier3D] that modifies the bone set in [method set_apply_bone] based on the transform of the bone retrieved by [method get_reference_bone]. Clear all settings. Returns the apply amount of the setting at [param index]. Returns the apply bone of the setting at [param index]. This bone will be modified. Returns the apply bone name of the setting at [param index]. This bone will be modified. Returns the reference bone of the setting at [param index]. This bone will be only referenced and not modified by this modifier. Returns the reference bone name of the setting at [param index]. This bone will be only referenced and not modified by this modifier. Returns the reference node path of the setting at [param index]. This node will be only referenced and not modified by this modifier. Returns the reference target type of the setting at [param index]. See also [enum ReferenceType]. Returns the number of settings in the modifier. Sets the apply amount of the setting at [param index] to [param amount]. Sets the apply bone of the setting at [param index] to [param bone]. This bone will be modified. Sets the apply bone of the setting at [param index] to [param bone_name]. This bone will be modified. Sets the reference bone of the setting at [param index] to [param bone]. This bone will be only referenced and not modified by this modifier. Sets the reference bone of the setting at [param index] to [param bone_name]. This bone will be only referenced and not modified by this modifier. Sets the reference node path of the setting at [param index] to [param node]. This node will be only referenced and not modified by this modifier. Sets the reference target type of the setting at [param index] to [param type]. See also [enum ReferenceType]. Sets the number of settings in the modifier. The reference target is a bone. In this case, the reference target spaces is local space. The reference target is a [Node3D]. In this case, the reference target spaces is model space. In other words, the reference target's coordinates are treated as if it were placed directly under [Skeleton3D] which parent of the [BoneConstraint3D].