code: @Nonnull
    public final UnifiedResponse setXFrameOptions (@Nonnull final EXFrameOptionType eType,
                                                   @Nullable final ISimpleURL aDomain)
    {
      ValueEnforcer.notNull (eType, "Type");
      if (eType.isURLRequired ())
        ValueEnforcer.notNull (aDomain, "Domain");
  
      if (eType.isURLRequired ())
        setCustomResponseHeader (CHttpHeader.X_FRAME_OPTIONS,
                                 eType.getID () + " " + aDomain.getAsStringWithEncodedParameters ());
      else
        setCustomResponseHeader (CHttpHeader.X_FRAME_OPTIONS, eType.getID ());
      return this;
    }
docs: The X-Frame-Options HTTP response header can be used to indicate whether or
  not a browser should be allowed to render a page in a &lt;frame&gt;,
  &lt;iframe&gt; or &lt;object&gt; . Sites can use this to avoid clickjacking
  attacks, by ensuring that their content is not embedded into other sites.
  Example:
  
  <pre>
  X-Frame-Options: DENY
  X-Frame-Options: SAMEORIGIN
  X-Frame-Options: ALLOW-FROM https://example.com/
  </pre>
  
  @param eType
  The X-Frame-Options type to be set. May not be <code>null</code>.
  @param aDomain
  The domain URL to be used in "ALLOW-FROM". May be <code>null</code>
  for the other cases.
  @return this
  @since 6.0.5