[gov2001-l] Question about cluster specification in survey library

Hi All. I'm trying to adjust for survey design factors in my reanalysis of replication data but am unsure about the cluster specification in the 'survey' library. In particular, I am not sure where/how to incorporate the cluster variable (each stratum in my sample contains 1-2 clusters). For anyone familiar with this library - if my cluster variable is 'RAEHSAMP', is it sufficient to provide the id argument with this variable? For example: hrs.sbp <- svydesign(id=~RAEHSAMP, strata=hrs.bpmeds$RAESTRAT, weights=hrs.bpmeds$R5WTRESP, data=hrs.bpmeds) The example in the help window uses a specification of 'dnum+snum' which makes little sense to me. Any clarification would be great. Thanks! Sheila