code: function(angle) {
  		// TODO this clears any scale, should we care?
  		var a = Math.cos(angle);
  		var b = Math.sin(angle);
  		this.matrix[0] = this.matrix[3] = a;
  		this.matrix[1] = (0-b);
  		this.matrix[2] = b;
  	}
docs: Set the z-axis rotation of the matrix.
  
  @param {Number} angle the rotation angle, in radians
  @preserve