how to use keywords

[otzen]

The documentation mentions "archive on keywords".
In the settings there is an option "Archive tagged (with keywords) "

But I find no settings regarding this mythical keyword. And also i find no explenation in the documentation.

Expected:

• Either: Settings to define keywords.
• or: Description on documentation on how this setting works

[Brummolix]

In Thunderbird you can mark an email with a keyword like "important".
The setting means:
checked - archive mails that have a keyword (it does not bother what keyword it has, just if it has some), after XXX days
not checked - do not archive such mails