Expanding and Collapsing Tables

Could someone point me in the right direction? How are those expanding and collapsing tables/blocks you see in portal sites such as Netscape Personal Homepage/Microsoft SharePoint programmed? Where you can either expand the table and content or collapse the table and content. It seems quite a bit more difficult than DHTML. I would like to code those features but am not sure what they are officially called or what they are written in. Could some one point me in the right direction. Thank you fordeciphering my post!!