Saved results, details

• four classes of saved results
  
  

  r class	general commands	summarize
  e class	estimation commands	regress
  s class	parsing commands	_pred_se
  n class	none of the above; default	generate

• command must be explicitly declared rclass, eclass, or sclass if it is to return results:

        program define mycmd6, rclass

• macros, scalars, and matrices may be stored