The previous sections described P/T sets as being lists; however, these discussions ignored what the individual elements of the list are. A better definition is that a P/T set is a list of arenas, where an arena consists of the processes, threads, and groups that are affected by a debugging command. Each arena specifier describes a single arena in which a command acts; the list is just a collection of arenas. Most commands iterate over the list, acting individually on an arena. Some CLI output commands, however, combine arenas and act on them as a single target.

An arena specifier includes a width and a TOI. (Widths are discussed later in this section.) In the P/T set, the TOI specifies a target thread, while the width specifies how many threads surrounding the thread of interest are affected.