6.8.2.4 Diary Group Parameters

When you create a new diary group, or visit one, gnus-diary automatically checks your group parameters and if needed, sets the summary line format to the diary-specific value, installs the diary-specific sorting functions, and also adds the different X-Diary-* headers to the group's posting-style. It is then easier to send a diary message, because if you use C-u a or C-u m on a diary group to prepare a message, these headers will be inserted automatically (although not filled with proper values yet).