code: function (angle) {
              if (angle !== 0) {
                  var a = this.val,
                      a00 = a[0],
                      a01 = a[1],
                      a02 = a[2],
                      a10 = a[3],
                      a11 = a[4],
                      a12 = a[5],
                      s = Math.sin(angle),
                      c = Math.cos(angle);
  
                  a[0] = c * a00 + s * a10;
                  a[1] = c * a01 + s * a11;
                  a[2] = c * a02 + s * a12;
  
                  a[3] = c * a10 - s * a00;
                  a[4] = c * a11 - s * a01;
                  a[5] = c * a12 - s * a02;
              }
              return this;
          }
docs: rotate the matrix (counter-clockwise) by the specified angle (in radians).
  @name rotate
  @memberOf me.Matrix2d
  @function
  @param {Number} angle Rotation angle in radians.
  @return {me.Matrix2d} Reference to this object for method chaining