man: doveconf - Document -F parameter

Author: sirainen

docs/core/man/doveconf.1.md

@@ -77,6 +77,32 @@ configuration in easy human readable output.
             This matches filters which were configured like:
             :   **remote 1.2.3.0/24 { # special settings }**
 
+**-F**
+:   Show the configuration in a filter-based format, which is how Dovecot
+    internally accesses it. This can be useful for debugging why configuration
+    is not working as expected.
+
+    The settings are grouped into different "structs", which are all accessed
+    independently. A new struct is started in the output as `# struct_name`.
+
+    Next is the list of filters, which begin with `:FILTER` followed by the
+    filter in the event filter syntax. An empty filter matches everything.
+    The filters are processed from end to beginning. The settings are taken
+    from the first matching filter (i.e. the last in the output). Since not
+    all filters have all settings defined, the processing continues until all
+    settings have been found.
+
+    Named list filter such as `protocols = imap pop3` are shown as
+    `protocol/imap=yes` and `protocol/pop3=yes # stop list`. The "stop list"
+    means that the value is not modified by any following filters that match.
+    If the setting was defined as `protocols { imap=yes, pop3=yes }`, the
+    "stop list" would be missing, because this setting is only adding the
+    protocols, not replacing the list.
+
+    Settings groups are included in `:INCLUDE` lines. The includes are
+    processed last, after all filters have been applied, so all settings inside
+    the groups can be overridden.
+
 **-h**
 :   Hide the setting's name, show only the setting's value.