docs: public void stepIn(final IonType containerType) throws IOException
      {
          if (!isContainer(containerType))
          {
              throw new IonException("Cannot step into " + containerType);
          }
          prepareValue();
          updateLength(preallocationMode.typedLength);
          pushContainer(containerType == STRUCT ? ContainerType.STRUCT : ContainerType.SEQUENCE);
          depth++;
          buffer.writeBytes(preallocationMode.containerTypedPreallocatedBytes[containerType.ordinal()]);
      }