The value of the SignedXml.XmlDsigXsltTransformUrl field is "http://www.w3.org/TR/1999/REC-xslt-19991116".
Use this field to conveniently supply a value to one of the URI attributes of an element used for XMLDSIG.
The System.Security.Cryptography.Xml.XmlDsigXsltTransform class implements the transform described by the SignedXml.XmlDsigXsltTransformUrl field.
For more information, see the World Wide Web Consortium (W3C) specification at http://www.w3.org/TR/1999/REC-xslt-19991116.