I have following questions to the DMRG tutorials. Why there is N in a line:

'CONSERVED_QUANTUMNUMBERS'  : 'N,Sz',

I understand that Sz stands for conserved quantum number but spin model on the open chain lattice does not have quantum number called N. 

Is this N added to 'CONSERVED_QUANTUMNUMBERS' just in case someone may use some bosonic model?

Bests,

Rafał