question about bench.c

Hi all,
i have a question about the example bench.c. i'm using 0.8.1 and libxml2 2 5.4

In this program, the domdoc is obtained, then its pointer is passed to a 
traversal routine that outperform the traversal of the tree, after doing a 
pointer cast to a GdomeElement.

What is not clear is: why this code works?

shouldn't be gdome_doc_documentElement needed to obtain the document element 
and then start the traverse from this node? if not, why the GDOME_EL macro 
evaluates false on the domdoc?

thanks for the help