A frame is a data frame or a non-empty ordered list of data frames.
A data frame and a one-element list containing it have the same meaning.
execute() also accepts separate data-frame arguments after frame.
Details
One hierarchy or separate registers
A single hierarchy contains the rows needed for the requested stages, including parent identifiers. Variables describing a selected cluster, such as its MOS and stratum, must be constant within that cluster. Separate registers describe one sampling level each and map positionally to the requested stages. List names label registers in messages. They do not reorder stages or define joins. Child registers carry the parent keys needed to identify eligible descendants.
Continuing fieldwork
Use execute(partial_sample, next_register) to resume the same design
after listing. The earlier selection and weights are retained. If one
supplied frame could cover either the next stage or several remaining
stages, specify stages to state which stages to execute.
Use execute(new_design, previous_sample) to select a new phase from an
earlier sample. This records an additional probability-sampling operation.
It is distinct from continuing the unfinished stages of a design.
Frame checks apply before selection: column names must be unambiguous, design variables must be present, and keys and cluster-level variables must satisfy the design's identity rules. A frame fingerprint in a saved design records the supplied data. It does not certify executability.