For purposes of protocol, emperors were once given precedence over kings in international diplomatic relations, but currently precedence amongst heads of state who are sovereigns—whether they be kings, queens, emperors, empresses, princes, princesses and to a lesser degree presidents—is determined by the duration of time that each one has been continuously in office. Outside the European context, emperor was the translation given to holders of titles who were accorded the same precedence as European emperors in diplomatic terms. In reciprocity, these rulers might accredit equal titles in their native languages to their European peers. Through centuries of international convention, this has become the dominant rule to identifying an emperor in the modern era.