The Liberalized Votings Rules which I posted a few days ago can more generally be referred to as Selection Rules. Various types of voting systems have been proposed. Among them are preferential voting and approval voting. The general topic is Rational Choice Theory.
The "DIS" vote was intended to indicate some dissatisfaction with or disapproval of a ballot measure. Often one feels the need for action on a particular issue and the measure may be defective is some manner. One may have legitimate doubts about a measure. "DIS" would be a way of indicating the position that the measure needs to be rewritten. Another name for "UND" might be "NOP" for "NO OPINION".
The President has the option of expressing disapproval for a bill before it becomes law by exercising his veto power. So why not grant voters a similar option in the case of initiatives and referendums. Badly written measures are a waste of time and disrupt the legal process.
Selections Rules can be applied to situations other than elections. For example, the choice of a person for a particular position, which computer one might like to buy or what present to get someone for Xmas.