A label for the group.
One or more log command labels, or one or more group command labels.
The group command lets you group any number of logs or groups. This allows you to give commands that refer to several logs at the same time, because a command specifying the label of a group will be applied to all the logs in that group or its sub-groups.
Groups can be made recursively (ie. groups of groups). Each group must contain either groups or logs, but not both; you are not permitted to have a group consisting of groups and single logs.
(group vat20 temp20 press20)
(group vat21 temp21 press21)
(group limits max_ht min_ht)
(group all vat20 vat21 limits)