Why doesn xsl:output work?
The Cocoon project doesn’t implement the xsl:output feature for XSLT because we believe it breaks the separation of concerns and doesn’t match the internal Cocoon architecture. On the other hand, we do understand the importance of specifying how the content should be presented to the requesting client. For this reason, Cocoon uses the cocoon-format processing instruction to tell the engine which formatter to use to format the transformation output.