[xsl] Default attribute values?

[Phillip B Oldham <phillip.oldham@xxxxxxxxxx>]

Hi again

I'm trying to add default attribute values to elements, but I get 
errors. Is there a simple way to do it using xpath? What i'm trying is:

<input type="text" value="{un|'Please enter your username'}" />

Is there a simple way of doing this, or do I have to throw an xsl:choose 
inside an xsl:attribute?