Only valid XML files are accepted and a run will fail if the xml parser (libxml2) finds the files invalid.
The numbers in the parenthesis denote the occurrence of an element.
We will use UML-like notation to represent the relationship between XML elements.
Children: project, (qmcsystem, particleset, wavefunction, hamiltonian, include)*,init?, qmc
Content: external XML file to be included
Note: The root element of an external file is qmcsystem