How does Matlab's implementation of Kruskal and Prim algorithms choose edges with the same weight and initial nodes?

Hi,

I was wondering how Matlab's implementation of Kruskal algorithm, decides which edge to choose as part of the MST when there are two (or more) edges with the same weight.

On the other hand, when no root is passed to Prim's algorithm, which node is chosen as starting point?

Thanks very much in advance for your help!

Cheers, Gregorio