And just in case anyone else missed it -
<xsl:message>some text here</xsl:message> will output "some text here" to the console, which is nice but not so useful.
<xsl:message terminate="yes">some text here</xsl:message>, on the other hand, will raise an expcetion with "some text here" as the message, which, unless handled, will cause the orchestration to get suspended and "some text here" written to the event log as part of the error, something like this:
Uncaught exception (see the 'inner exception' below) has suspended an instance of service '********************'.
The service instance will remain suspended until administratively resumed or terminated.
If resumed the instance will continue from its last persisted state and may re-throw the same unexpected exception.
Shape name: Construct Response set
Exception thrown from: segment 5, progress 37
Inner exception: Transform terminated: 'some text here.'.