In principle another family member has first shot at the job, but the Wagners snap and snarl at one another with a ferocity that makes the Dallas and Denver clans look blissful.

ECONOMIST: Athens beats Sparta by an ear

In 2003, UNESCO's General Conference adopted a "Charter on the Preservation of the Digital Heritage", a declaration of principle designed to assist Member States in preparing national policies to preserve, and provide access to, digital heritage.

UNESCO: Communication and Information

This established the principle of mutual recognition: that goods sold in one member state could be sold in all.

ECONOMIST: Are regional trade agreements a good idea?

Fatah has supported the peaceful two-state principle since the late 1980s, but half the 11-member Central Council opposed the terms of the agreement with Israel negotiated secretly in the Norwegian capital.

ECONOMIST: Palestine

The union, keen that its activities should be bankrolled by member countries, has eschewed the "begging bowl" principle.

BBC: Profile: African Union

It is a matter of constitutional principle that the chancellor does not act without an unambiguous request from a member to relinquish his or her seat.

BBC: Hilary Benn issues challenge to rules on MP resignation

The Green Party - which is a member of the left-wing government - is opposed in principle to a third airport, arguing that it should be sited in the provinces to encourage decentralisation.

BBC: Paris plans third airport

Europe's governing body is keen to introduce a rule preventing the international transfer of players under the age of 18 after member associations, clubs, leagues and players agreed to the principle at a March meeting.

BBC: Man Utd deny 'stealing' youngster

The tax will apply if any party to the transaction is based in a participating member state, regardless of where the transaction takes place - the so-called "residence principle" - and it is this provision that is causing the most controversy.

BBC: Financial transaction tax tabled by European Commission