Quick introduction to the HTML DOM selection API.
sel.removeAllRanges() // deselects
sel.addRange(range) // sets a selection
sel.removeRange(range) // remove a range
sel.rangeCount
sel.getRangeAt(0) // get the 0th range
sel.collapse(parent, offset)
sel.collapseToEnd()
sel.collapseToStart()
sel.isCollapsed
sel.containsNode(node)