Sign the XML document

To sign the document in whole, you need to setup an instance of TElXMLReference (see the corresponding how-to article) as follows:

• if the external document is encrypted, load the document to TElXMLDOMDocument and set URI property to the URI of the document. Otherwise just set URI property to empty value
• set URINode property to reference the first node of the document, which is of type TElXMLDOMElement.