2.2.14 [W3C-XSLT] Section 16, Output
An XSLT processor may output the result tree as a sequence of bytes, although it is not required to be able to do so (see [W3C-XSLT] [17 Conformance]). The xsl:output element allows stylesheet authors to specify how they wish the result tree to be output. If an XSLT processor outputs the result tree, it should do so as specified by the xsl:output element; however, it is not required to do so.
MSXML3 and MSXML6
The processor does not produce the result tree as a sequence of bytes.