Root element of the document identifying it as an HML message. Must 
          contain the version of HML that the modeled data in this document 
          uses.
        Children:
        ---------
        - property (optional, qty: 0 or more)
        - hmlid    (optional, qty: 1)
        - reporting-center (optional, qty: 1) - Required for NMDP samples
        - sample (required, qty: 1 or more)
        - typing-test-names (optional, qty: 0 or more)
        Attributes:
        -----------
        - version:       Version of HML the document follows (required)
        - project-name:  Name of the typing project (optional) |