clipAction( clip, optionalRoot, blendMode ) {

		const root = optionalRoot || this._root,
			rootUuid = root.uuid;

		let clipObject = typeof clip === 'string' ? AnimationClip.findByName( root, clip ) : clip;

		const clipUuid = clipObject !== null ? clipObject.uuid : clip;

		const actionsForClip = this._actionsByClip[ clipUuid ];
		let prototypeAction = null;

		if ( blendMode === undefined ) {

			if ( clipObject !== null ) {

				blendMode = clipObject.blendMode;

			} else {

				blendMode = NormalAnimationBlendMode;

			}

		}

		if ( actionsForClip !== undefined ) {

			const existingAction = actionsForClip.actionByRoot[ rootUuid ];

			if ( existingAction !== undefined && existingAction.blendMode === blendMode ) {

				return existingAction;

			}

			// we know the clip, so we don't have to parse all
			// the bindings again but can just copy
			prototypeAction = actionsForClip.knownActions[ 0 ];

			// also, take the clip from the prototype action
			if ( clipObject === null )
				clipObject = prototypeAction._clip;

		}

		// clip must be known when specified via string
		if ( clipObject === null ) return null;

		// allocate all resources required to run it
		const newAction = new AnimationAction( this, clipObject, optionalRoot, blendMode );

		this._bindAction( newAction, prototypeAction );

		// and make the action known to the memory manager
		this._addInactiveAction( newAction, clipUuid, rootUuid );

		return newAction;

	}
Returns an instance of {@link AnimationAction} for the passed clip.

If an action fitting the clip and root parameters doesn't yet exist, it
will be created by this method. Calling this method several times with the
same clip and root parameters always returns the same action.

@param {AnimationClip|string} clip - An animation clip or alternatively the name of the animation clip.
@param {Object3D} [optionalRoot] - An alternative root object.
@param {(NormalAnimationBlendMode|AdditiveAnimationBlendMode)} [blendMode] - The blend mode.
@return {?AnimationAction} The animation action.