XPath to return default value if node not present

Question

Say I have a pair of XML documents

    
    mystring

and

Answer 1

In XPath 1.0, use:

concat(/Foo/Baz,
       substring('not-found', 1 div not(/Foo/Baz)))

If you want to handle the posible empty Baz element, use:

concat(/Foo/Baz,
       substring('not-found', 1 div not(/Foo/Baz[node()])))

With this input:

Result: not-found string data type.