authering tools, shared borders

Can any one help me with information on "shared borders". I've been asked in
relation to Frontpage 2000 and accessibility. 

Kind regards
Helle Bjarno
Videncenter for Synshandicap / Visual Impairment Information Centre
Rymarksvej 1, DK-2900 Hellerup, Denmark
tlf: +45 39 40 31 00
fax: +45 39 61 94 14
e-mail: hbj@visinfo.dk / visinfo@visinfo.dk
URL: www.visinfo.dk