code: @Nonnull
    public SchematronResourcePure setPhase (@Nullable final String sPhase)
    {
      if (m_aBoundSchema != null)
        throw new IllegalStateException ("Schematron was already bound and can therefore not be altered!");
      m_sPhase = sPhase;
      return this;
    }
docs: Set the Schematron phase to be evaluated. Changing the phase will result in
  a newly bound schema!
  
  @param sPhase
  The name of the phase to use. May be <code>null</code> which means
  all phases.
  @return this