You sometimes need to specify a reference to a note relative to something else, like the current note. Group designators are a set of generic relative references to, or placeholders for, a group [sic] of notes whose actual identity is context sensitive. Group designators are written with lower case starting letters and intercapitalised if multiword; e.g. sibling. Usage is case sensitive.
Unlike item designators, group designators may not be use for specifying attribute path references.
Thus, for a word count of the current note's children you use:
$MyCount=sum(descendants,WordCount)
In older versions this would have required using an export code:
$MyCount=^sum(descendants,WordCount)^
Some action operators and export codes work on groups of notes. These can use group designators in place of literal lists (or attribute-stored lists).
If a group is empty - e.g. the current note has no children, the group operator returns the equivalent value/boolean for the current note instead.