There are several ways to implement open-list systems, from an option of a single preference for a candidate within the selected list to possibilities for crossing lists. There are also systems where the candidates are not selected from predefined lists but rather from nomination districts as in Denmark and Romania. In Denmark, parties may choose to have predefined lists. Therefore, the candidates may or may not be ranked by the parties. In Denmark (for those parties not having a predefined list) and Romania, the candidates running in nomination districts are not ranked across the districts. There may be also candidate lists which are alphabetical or listed in any another mode of classification, and it is up to the voter to decide who should fill party’s seats.