code: @Nonnull
    public SchematronResourcePure setFunctionResolver (@Nullable final XPathFunctionResolver aFunctionResolver)
    {
      if (m_aBoundSchema != null)
        throw new IllegalStateException ("Schematron was already bound and can therefore not be altered!");
      m_aFunctionResolver = aFunctionResolver;
      return this;
    }
docs: Set the function resolver to be used in the XPath statements. This can only
  be set before the Schematron is bound. If it is already bound an exception
  is thrown to indicate the unnecessity of the call.
  
  @param aFunctionResolver
  The function resolver to set. May be <code>null</code>.
  @return this