Interpreting keywords

[Mark Foley]

I've marked several messages in Thunderbird using tags. Tags used are:

0 Important
1 Work
2 To Do
3 Personal
4 Later

The messages so tagged appear to have the flag fields set in the IMAP Maildir:

cur/1449002162.8993_0.mail:2,Sb
cur/1449001929.28087_0.mail:2,Sad

I've looked in dovecot-keywords and find:

$ more dovecot-keywords 
 0 $label1
 1 $label2
 2 $label3
 3 $label4
 
I assume these "$label" values are macros that possibly refer to "Important", "Work", etc., but
where are these $label's defined? Are they defined in the dovecot configs somewhere or does the
mail client just "know" what these correspond to?

--Mark