hybrid {be} and {bei}: sumti link to attached sumti to a selbri, repeatable, valid for both first and subsequent attachments.
be is only for the first attachment, and bei is only for non-first attachments. bei'i is valid for either the first or subsequent attachments, and is terminated with be'o. See also bei'e, to automatically apply bei'i to all following sumti until terminated with be'o; this also can be used after SEI cmavo to attach following sumti to the SEI cmavo without having to explicitly use be or bei to sumti that occur after the selbri (sumti preceding the selbri in the case of sei are already part of the SEI clause).