What is it?
A KeyWords cluster, like a WordList cluster, represents two or more words which are found repeatedly near each other. However, a KeyWords cluster only uses key words.
A screenshot will help make things clearer. This is a key words list based on a piece of transcript from a Wallace and Gromit film, using the BNC as the reference corpus.
The clusters tab below shows us something like this:
The frequency 3 in the GROMIT OH line means that there are 3 cases where the key-word GROMIT is found within the current collocation span of OH in that text. [.] means that there is typically one intervening word or [..] two intervening words as in this case shown from the source text.
The procedure is text-oriented. You can only get a keywords cluster list if there is exactly one source text. Note that for this procedure sentence boundaries are not blocked, so Gromit and Ah can be considered to have one word Oh intervening.
See also: Plot calculation.