How do I get all of a particular type of nodes in Gumbo Parser?

Question

I am trying to use Gumbo Parser to get all the nodes of a particular type - like all <p></p> nodes or all <a href...></a> nodes from a HTML document.

My function prototype is like following:

list<GumboNode*> GetAllNodesOfType(GumboNode* root, <required type of nodes> )

What should I put in the place of second parameter <required type of nodes>?