What’s this all about: a vertical menu with submenus which are hidden initially and show on rollover.
1. On roll-over over a zero-level element, the corresponding sub-menu must appear
2. On roll-over over another zero-level element, besides the effect from point 1. any other secondary menu must hide, only the the submenu corresponding to the active roll-over must remain visible
The most elegant solution I found is in the page linked at the beginning of the article, but it was a bit too long for what I needed, so I took it, adapted it, and I got exactly what I need (see here a functioning example, with all it needs to understand it, if you look in the source).
Later edit: for a more elegant menu version (in terms of coding and approach), but less functional and without JS, read here (in Romanian).
Versiunea in Romana a acestui articol aici.