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#### 2.16.2 Topic Variables

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:

‘`i`’
  Indentation.
‘`n`’
  Topic name.
‘`v`’
  Visibility.
‘`l`’
  Level.
‘`g`’
  Number of groups in the topic.
‘`a`’
  Number of unread articles in the topic.
‘`A`’
  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.

The `gnus-topic-display-empty-topics` says whether to display even topics that have no unread articles in them. The default is `t`.