A grpprl is a data structure that records a set of sprms. The 0th sprm is recorded at offset 0 of the structure. Any succeeding sprms are recorded immediately after the end of the preceding sprm . To traverse a grpprl and locate the sprms recorded within it, it's necessary to fetch the opcode of the first sprm, lookup the length of the sprm with that opcode, use that length to skip past the first sprm, fetch the opcode of the second sprm, lookup the length of that sprm, use the length to skip the second sprm, and so on. See the table in the "SPRM Definition" topic to determine the length of a sprm.
The phrase "apply the sprms of a grpprl (or papx or sepx)" used later in this document means to fetch the 0th sprm recorded in the grpprl and perform the action for that sprm, fetch the first sprm and perform its action, and continue this procedure until all sprms in the grpprl (or papx or sepx) have been processed.