Filters are used to hide database rows which match or do not match a set of specified rules. The creation and management of filters is done via a database file's Advanced Filter... menu item. Saved filters are available from the context menu's Hide Items Matching Saved Filter and Hide Items Not Matching Saved Filter submenus.
The operation of the Filter Editor which is shared with database filters is described in The Filter Editor.
You can filter on any database column except the transient Results column.
An operator's value field can contain many of escape sequences described in Escape Sequences. (Only those which make sense in the context of a database). This allows you to compare columns against others, etc. The supported escape sequences include Date & Time sequences to make it easy to offset dates when matching.
The text regular expression operator's value field does not support escape sequences. All escape sequences are assumed to be regular expression escape sequences. You can test a regular expression via the preview button to the right of the field.