The method attribute on xsl:output identifies the overall method that should be used for outputting the result tree. The value must be a QName. If the QName does not have a prefix, then it identifies a method specified in this document and must be one of xml, html or text. If the QName has a prefix, then it is expanded into a URI reference using the namespace declarations in effect on the xsl:output element; the expanded name identifies the output method; the behavior in this case is not specified by this document. The default for the method attribute is chosen as follows. If the root node has an element child, the expanded name of the first element child of the root node (i.e. the document element) has local part html (in any combination of upper and lower case) and a null namespace URI, and any text nodes preceding the first element child of the root node contain only whitespace characters, then the default output method is html; otherwise, the default output method is xml. The default output method should be used if there are no xsl:output elements or if none of the xsl:output elements specifies a value for the method attribute.