If your output is really as specified then it's wrong: the "abc" prefix shouldn't appear unless there is an xmlns:abc="..." namespace declaration. If the "abc" prefix is bound to the XSLT namespace URI, then all is well (prefixes aren't important, only URIs).
Transformer isn't a class, it's an interface. There are several products that implement this interface. What's significant is the implementation you are using. You can discover this by using <xsl:value-of select="system-property('xsl:vendor-url')"/>
Michael Kay
http://www.saxonica.com/
Author, XSLT Programmer's Reference and XPath 2.0 Programmer's Reference