Some senior Hong Kong figures have spoken about unfulfilled treaty promises made between Britain and China. Yet the Sino-British Joint Declaration of 1984 says nothing about choosing Hong Kong's Chief Executive by the votes of five million people. The document which matters here is Hong Kong's Basic Law.
Prior to the handover in 1997, the colonial government expended considerable effort in democratising Hong Kong's Legislative Council or "LegCo". This process, that commenced in earnest in 1984 in the form of a Green Paper, and subsequently in a White Paper, nonetheless had to await the outcome of discussions between 23 representatives of Hong Kong and 36 representatives from Beijing on the enactment of a Basic Law.
No colonial-led reform in the run-up to the handover which did not converge with the Basic Law, in which Britain had no hand in the making, would have been practicable as the Basic Law would apply after the handover.
Dubbed a "mini-Constitution" for Hong Kong, the Basic Law is no treaty, and is a document no more sacred than a piece of Mainland Chinese legislation.
But when Lord Chris Patten, Britain's last governor of Hong Kong, proposed the reform of LegCo elections in a speech in October 1992, during LegCo's opening session, he acknowledged that such reforms will have to conform not only to the Joint Declaration but also the Basic Law.
That was the colonial government's understanding, notwithstanding Lord Patten's own, substantial and controversial efforts to democratise LegCo.
In treaty terms, if Britain condescended to look to the Basic Law for guidance on the practical implementation of the Joint Declaration, then it may be said that this is how the Joint Declaration should also be interpreted.
In practical legal terms, all roads lead to the Basic Law, what it says and how it should be interpreted. It is also the Basic Law which provides for the possibility of a democratically elected Chief Executive; the colonial government having shown no interest in replacing the governor with such a person.
Ultimate aim and ultimate authority
It is the Basic Law which says in Article 45 that "the ultimate aim is the selection of the Chief Executive by universal suffrage upon nomination by a broadly representative nominating committee in accordance with democratic procedures".
But the ultimate legal authority to interpret that ultimate aim lies with the Standing Committee of the National People's Congress (NPCSC), a body which is also vested with legislative power under Chinese socialist legality.
In order to understand the NPCSC's role, we need to return to Article 45, which states: "The method for selecting the Chief Executive shall be specified in the light of the actual situation" in the Hong Kong Special Administrative Region "and in accordance with the principle of gradual and orderly progress".
Annex I of the Basic Law adds that "if there is a need" to amend the selection method "for the terms subsequent to the year 2007" - there may be none - such an amendment must be endorsed by a two-thirds majority of LegCo, and the consent of the present Chief Executive, "and they shall be reported to" the NPCSC "for approval".
The first thing the NPCSC did, in 2004, was to interpret Annex I by requiring the Chief Executive to make a recommendation to the NPCSC before tabling an amendment before LegCo.
But in that year, the NPCSC also rendered a decision precluding any reform by 2007.
It explained that in the light of the need to address the "actual situation", and the principle of "gradual and orderly progress", it had found that while some wanted reform by 2007, there was nevertheless no broad consensus within Hong Kong society to move forward with reforms.
In the following year, the second Chief Executive, Mr Donald Tsang, proposed enlarging the current election committee which elects the Chief Executive from a body of 800 to 1,600 people. His proposal was defeated in the LegCo.
It was not until 2007 that consultations began anew with the issuance of a Green Paper, leading to another decision by the NPCSC in 2007.
In that decision, again the existing system was preserved for electing the Chief Executive in 2012. But the NPCSC did add that election by universal suffrage may take place in 2017.
Thus began a new consultation process last year which culminated in the fateful decision of the NPCSC of Aug 31 this year.
This decision envisages "two to three" candidates, requires a majority vote of the 1,200 members to secure a candidature, and provides for an election by all of Hong Kong's voters in 2017.
Basic Law as starting point and end point
It may be that this latest decision goes too far in restricting nominations for the 2017 election. Some might even ask how, if the Basic Law is so important, that it has only got us here. But it is not difficult to imagine the general satisfaction which the drafters of Article 45 must have felt. Seven years after the Basic Law was passed, a mere 400 people went on to elect the first Chief Executive. Seventeen years on, the average age of today's student protester, Beijing not only says that Hong Kong can have universal suffrage but also that it will.
In recent weeks, however, the Basic Law has been quoted in the press as if it had emerged from Alice's Looking Glass World - no more than a source of fallow phrases from which we pick the ones we want to mean whatever we want. This comes from the Basic Law saying too little with hopeful but scant words ("universal suffrage", "democratic procedure" and a "broadly representative" nominating committee) and too much at the same time (by referring to the "actual situation in Hong Kong", "gradual and orderly progress", having a democratically elected Chief Executive as merely an "ultimate aim", and by requiring a "nominating committee").
This only makes it more important for those opposed to the NPCSC to state their own interpretation, with articulacy and not simply hope, desire and disappointment. As Sir David Akers Jones once described it, we cannot descend into a debate scripted by Messrs Gilbert and Sullivan - "that's what it says", "no it doesn't", "yes it does", "No. It doesn't". The NPCSC is the ultimate authority on what the Basic Law means, but it does not have carte blanche. The NPCSC cannot say that the Basic Law is a cucumber from Mars.
Once the dust settles, the people of Hong Kong - protesters and others - may realise the significance of this truth, and find a need to return to the Basic Law, both as a starting point and for the end point upon which the very foundations of their current and future actions and beliefs rest.
That starting point would be the right to vote and stand for elections under the Basic Law and the Hong Kong Bill of Rights, including the Basic Law's guarantee that an international treaty, the International Covenant on Civil and Political Rights, shall apply.
These legal statements of right will have to be read with Article 45, and if the question comes before the courts, it could give pause and breathing room for all.
In my Law Of The Hong Kong Constitution with Johannes Chan, we had anticipated incredulity that we, together with our colleagues, have somehow succeeded in producing a thousand pages of fiction. So we began by explaining that a "Hong Kong Constitution" does exist because all parties - in Hong Kong and Beijing - consider the Basic Law to be so, and because the public issues of the day are debated according to its terms.
Yet such debate has become muted amid the sounds of the fiercest political controversy which Hong Kong has had to bear in recent memory. The Basic Law has fallen behind Twitter and Instagram, and has no purchase in the makeshift tents in Connaught Road.
If Hong Kong's age of restrained constitutional debate has now passed, unnoticed, beneath a sea of umbrellas, and is to be surpassed by university seminars on civil disobedience, then this would signify more than the passing of an era.
It would mark the demise of a shared framework for public-political debate which has been credited for post-handover Hong Kong's spectacular success.
Lim Chin Leng is Professor of Law at the University of Hong Kong, Visiting Professor at King's College London, a practising London barrister and member of Hong Kong's Committee on Pacific Economic Cooperation. The second edition of Law Of The Hong Kong Constitution will be published by Sweet & Maxwell next year.