Added in 1.9.0
/sline [-ar] <#channel> <N|nick>
Selects or de-selects lines in a channel nickname listbox. It can select either the Nth nickname in a listbox, or a specified nickname.
-a - Appends selection to current selection.
-r - Deselects instead of selects.
<#channel> - Channel where the listbox is located.
<N|nick> - Nick or the Nth nick to select.