code: public Matrix3x2fStack pushMatrix() {
          if (curr == mats.length) {
              throw new IllegalStateException("max stack size of " + (curr + 1) + " reached"); //$NON-NLS-1$ //$NON-NLS-2$
          }
          mats[curr++].set(this);
          return this;
      }
docs: Increment the stack pointer by one and set the values of the new current matrix to the one directly below it.
  
  @return this