Set variable using decode-esque statement

Trying to set a variable in an RTF for a watermark to distinguish a check being printed in PROD vs DEVL. 

The instance name is in the XML. 

The watermark text is set to <?$wMark?>

I'm trying to populate wMark based on a condition (null when instance name is PROD, DEVL/TEST when instance name is DEVL/TEST)

This works, but it's either DEVL or Null -- would like to have something for TEST as well. <xsl:variable name=”wMark” select=”xdoxslt:ifelse(INSTANCE_NAME=’DEVL’,’DEVL',’’)”/>

So I'm trying something like

<xsl:variable name="wMark" select="xdofx:decode('INSTANCE_NAME’,’DEVL’,’Development’,’TEST’,’Test’,’PROD’,'','')"/>