When the president of Legco could vote
Legislative Council president Tsang Yok-sing has caused controversy with his announcement that he would resign from the post, if needs be, to vote in favour of the political reform package sponsored by the Hong Kong government. The controversy arises because of the well-established convention that the president normally does not vote, and Tsang's undertaking, when he became president, that he would respect this convention.
Tsang has probably done Hong Kong a favour by shining a light on a significant incongruity between the Basic Law and the convention that governs voting by the Legco chief. The Basic Law spells out, in Articles 71 and 72, that Legco will have a president and the scope of his powers - but it puts no limits on the president's right to vote.
That restriction arises from a Legco constitutional convention, devolved from Britain, which has applied since well before 1997. In essence, it says the president customarily should not vote on any matters before Legco. Like the Speaker of the British House of Commons, the president is meant to preside over debates, maintain order and punish members who break the rules of procedure.
British experience dating back to the 14th century has shown that, to be effective, Speakers need to consistently conduct themselves in a non-partisan way. That has proved to be crucial in terms of retaining cross-party respect both for the office and the person who holds it.
Some limited exceptions to the ban on Speakers voting have emerged - mainly to break deadlocks - but any such voting must be done as uncontroversially as possible.
Annex I and II of the Basic Law set out the model for democratic reform in Hong Kong. We are going to see a series of votes in Legco related to them in the coming years and, due to their singular and critical nature, it would be sound to have an exception to the convention allowing presidents to cast ballots in Annex I and II votes.
Apart from this exception, the general rule that the president does not vote would prevail - coupled with the convention that the president should not advocate or take sides on other issues.
A member of the pan-democrat camp may someday be voted in as president. In that case, a presidential vote might turn 39 votes in favour of abolishing functional constituencies into the 40 votes - or a two-thirds majority - needed to secure this worthwhile outcome.
This approach would take into account Hong Kong's current constitutional circumstances, which did not apply before 1997. It would allow the president - who will probably be directly elected - to represent those who elected him or her on this crucial issue.
The closely drawn exception - which tracks the Basic Law - provides a means to resolve the current, inherent tension between the Basic Law and the presidential voting convention in an open and even-handed way. Tsang's announcement has laid the initial foundations on which this exception might be established, either by formal resolution or by acceptance.
Richard Cullen is a visiting professor in the Faculty of Law at Hong Kong University