[xsl] Adding duration to date

["tom tom" <tomxsllist@xxxxxxxxxxx>]

I wish to add a duration to a date, something along the lines of:

<xsl:value-of select="current-date() + xdt:yearMonthDuration('P6D')"/>.

I am using saxon 8.x, what is the correct way to do this, what should my 
namespace declarations be to make this work and does the way I do this 
depend on which version of Saxon / another processor I am using?

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