code: @Nonnull
    public SchematronResourcePure setEntityResolver (@Nullable final EntityResolver aEntityResolver)
    {
      if (m_aBoundSchema != null)
        throw new IllegalStateException ("Schematron was already bound and can therefore not be altered!");
      internalSetEntityResolver (aEntityResolver);
      return this;
    }
docs: Set the XML entity resolver to be used when reading the Schematron or the
  XML to be validated. 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 aEntityResolver
  The entity resolver to set. May be <code>null</code>.
  @return this
  @since 4.1.1