doveadm-search-query pattern format

Hello,

the doveadm-search-query documentation specifies a 'pattern' for many search keys. Unfortunately it does not mention the format specification of this pattern (special characters, wildcards, ...). I'm using dovecot 2.2.9 but also searched the current documention on dovecot.org.

Where can I find further documentation concerning the exact specification of the pattern format?