The previous section told you how to tell Gnus which topics to display. This section explains how to tell Gnus what to display about each topic.
The topic lines themselves are created according to the
gnus-topic-line-format variable (see Formatting Variables).
Valid elements are:
Number of groups in the topic.
Number of unread articles in the topic.
Number of unread articles in the topic and all its subtopics.
Each sub-topic (and the groups in the sub-topics) will be indented with
gnus-topic-indent-level times the topic level number of spaces.
The default is 2.
gnus-topic-mode-hook is called in topic minor mode buffers.
gnus-topic-display-empty-topics says whether to display even
topics that have no unread articles in them. The default is