This reference describes every method in the HTML_QuickForm_advmultiselect class.
In a two multi-select boxes default shape, there are :
a list with all unselected values (on left side)
a list with all selected values (on right side)
two buttons (add, remove) to swap items from one list to the other (on middle side)
optional headers for each list
In a single multi-select box default shape, there are :
a list with all values (selected: checkbox on, unselected: checkbox off)
none buttons
optional header for the list
Buttons (up, down) to sort item are unavailable in a single multi-select box shape.
In a two multi-select boxes custom shape, you may also have :
two buttons to sort selected item (by user-end)
There are no order between setting button (up, down) attributes and setting placeholders {moveup}, {movedown} into the template.