The trigger will only activate for tasks whose reference matches the regular expression. No filtering will be done if left blank.
The eventual regexp matching groups will be exported to the KANBOARD_TASKREF_{index of group} environment variables.
For example:
The regular expression ([A-Z]+)-([0-9]+)
will match the reference ABC-12345
and will export the following environment variables:
KANBOARD_TASKREF=ABC-12345
KANBOARD_TASKREF_0=ABC
KANBOARD_TASKREF_1=12345