how to find the order of joins from Explain command XML plan output in PostgreSQL9.3.4

"EXPLAIN (format XML) <query>" command in PostgreSQL9.3.4 gives the plan
chosen by the optimizer in XML format. In my program, I have to extract
certain data about optimizer plan from this XML output.

I am using *LibXML2* library for parsing the XML. I had successfully
extracted information about which relations are involved and what joins are
used by parsing the XML.
But I am *unable to extract the* *order of joining the relations from
the XML output*. I conceptually understood that the level order traversal
of binary tree representation of the XML plan will give correct ordering of
joins applied.
But I could not figure out how do I get that from the XML? Does
libXML2 support anything of this sort? If not how should I proceed to
tackle this?