Internal is the internal subset, given as a string. If there was no internal subset, it will be undefined. Internal will contain all whitespace, comments, processing instructions, and declarations seen in the internal subset. However, comments and processing instructions will not appear if they've been processed by their respective handlers. This handler is called for xml declarations.
Version is a string containg the version.
Encoding is either undefined or contains an encoding string. Standalone will be either true, false, or undefined if the standalone attribute is yes, no, or not made respectively. This just prints out the document in outline form. Nothing special is returned by parse. Each time an element starts, a sub by that name in the package specified by the Pkg option is called with the same parameters that the Start handler gets called with.