[basex-talk] xquery replace

I am trying to use xquery replace but cannot, it seems, figure out the correct syntax. As I understand it, the replace query should be of the form: "xquery replace expr with node", so I'm trying to do the following:

xquery replace root()/child with <child>new data</child> Stopped at line 1, column 15: Syntax: XQUERY [query] Evaluate XQuery.

I've tried a number of variations but I get the same error. Any ideas? Thanks. -tjw