Heh! I wasn't saying you were ambiguous; I meant that "XML" can mean the system of nodes that is an XML document; a string that is a representation of that doc

Heh! I wasn't saying you were ambiguous; I meant that "XML" can mean the system of nodes that is an XML document; a string that is a representation of that document; and the specific string that was parsed to create the document. An infinite number of strings can describe the same document, because there is the concept of ignorable whitespace when parsing XML. So "XML" is ambigous because the acronym could mean any of several things; and ambiguous the other way, because XML allows multiple string representations of the same object. [Edit] So I don't know how you can sign an "XML document"; the only thing I know how to make a signature for is a specific serialization of that document. May be someone's invented a way of signing the abstract document object, but I haven't heard of it.