Required library edition:
Required library file: dhtmlxcombo.js

enables the filtering mode

• mode - (boolean or 'between') enables the filtering mode (see details below)
• url - (string) url for filtering from XML, optional
• cache - (boolean) XML caching, optional
• autosubload - (boolean) enable auto load additional suggestions on selecting last loaded option

The 'between' value sets the mode at which the combo searches for any occurrence of the typed text in items (in contrast to other modes that perform searching from the item's beginning).
Also the 'between' mode isn't supported by dhtmlxConnector. So if you decide to use it and deal with the server, you will need to provide a fully custom server-side solution.