Documentation for /usr/lib/dovecot/imap executable

[Christoph Groth]

Dear Dovecot experts,

I'm in the process of setting up dovecot with mbsync as a local 
cache for remote IMAP servers. One recipe that I found involves 
using the /usr/lib/dovecot/imap (This is with Debian's dovecot 
package).  For example, in .mbsyncrc I have

IMAPAccount cwg-wf-local
RequireSSL no
Tunnel "/usr/lib/dovecot/imap -o 
mail_location=maildir:/home/cwg/.mail/cwg-wf"

This works, but I wonder: is there any documentation for the 
/usr/lib/dovecot/imap executable?  What options does it take?  If 
there's no documentation: where can I find this command in 
dovecot's sources?

Thank you,
Christoph