WHEN China ratified the United Nations law of the sea treaty in 1996, it was hailed as an important step towards stability and peaceful settlement of disputes in East Asia's vast, valuable but conflict-riven offshore zone.
So the move by the Philippines last week to turn to the UN for a judgment on whether China's sweeping claims to nearly all of the South China Sea is in line with the 1982 treaty seemed like a perfectly law-abiding step.
When Beijing ratified the treaty establishing the legal framework for conduct in the world's oceans and seas, known as the UN Convention on the Law of the Sea (Unclos), it registered some points about the application of the treaty, as member states are entitled to do.
Two of the points are relevant to the launch by the Philippines of Unclos arbitration proceedings against China.
The first is that in ratifying Unclos in 1996, China reaffirmed sovereignty over all its archipelagos and islands listed in Article 2 of a 1992 law adopted by the National People's Congress, China's legislature. This law on the territorial sea and the contiguous zone states that the land territory of China includes the mainland, its coastal islands, and some other groups of islands.
Those enumerated in the last category are Taiwan - which China regards as a rebel province - and the nearby Diaoyu (Senkaku) islands in the East China Sea. The Senkakus are administered by Japan but bitterly contested by China.
In the South China Sea, the islands belonging to China under the 1992 law are, from north to south, the Dongsha (Pratas) islands, occupied by Taiwan; the Xisha (Paracel) islands, occupied by China but claimed by Vietnam; the Zhongsha (Macclesfield Bank) islands; and the Nansha (Spratly) islands, over which China, Taiwan, Vietnam, the Philippines and Malaysia have conflicting claims.
The second point registered with Unclos by China came 10 years later in 2006, when Beijing gave notice, as it was entitled to do, that it did not accept any international court or arbitration in disputes over maritime boundaries, islands or military activities.
China has said this is a question of Chinese sovereignty, not international law of the sea, and that the former, established for centuries by prior occupation and administration, must take precedence over the latter.
In April last year, as China and the Philippines struggled for control of Scarborough Shoal anchorage and fishing grounds, which Manila says is within its Exclusive Economic Zone (EEZ) established by Unclos, Chinese Embassy spokesman Zhang Hua in Manila acknowledged that the treaty allowed countries to have EEZs but said they could not exercise sovereignty over areas within those waters that were owned by other countries, in this case China.
Beijing ignores the fact that no other country recognises its South China Sea claims, although Taiwan maintains a similar position in its East and South China Sea claims to that of Beijing.
In 2009, China sent a letter to UN Secretary-General Ban Ki Moon saying that it had "indisputable sovereignty over the islands in the South China Sea and the adjacent waters, and enjoys sovereign rights and jurisdiction over the relevant waters as well as the seabed and subsoil thereof".
Attached was a map showing China's claim, marked by a nine-dash line stretching as far south as James Shoal, just 80km from Malaysia's Bintulu in Sarawak, and about 1,800km from the Chinese mainland. A Xinhua report in April last year described the shoal as "the southernmost point of China's territory".
China's use of its nine-dash line claim to support its South China Sea claims, and its references to "historic rights" inside this imprecisely defined line, have provoked controversy and given South-east Asian claimants the opportunity to argue that China is not acting in conformity with Unclos and international law.
The Philippines is also asking for a ruling that China bring its domestic law into conformity with its obligations under Unclos, and that Beijing desist from violating Philippine rights in its maritime domain.
United States law professor Julian Ku, who follows the issue closely, said in his blog last week that Manila's case is the most important ever to have been filed under the dispute resolution procedures of Unclos.
"I don't think that the Philippines has a hopeless case but I do think they will face a huge challenge to get any arbitral tribunal to assert jurisdiction here, especially since one judge will be appointed by China," he wrote.
But Prof Ku added that if Manila managed to get past the jurisdictional hurdle, it would have "a very good chance of prevailing since China's claim is hard to square with the rest of Unclos".
Unclos defines the rights and jurisdiction of China in maritime zones subject to its sovereignty, namely its internal waters and territorial sea, a belt stretching out nearly 19km from its coast.
The treaty also defines China's authority in maritime areas outside its sovereignty, zones which can stretch 370km or more from the coast.
Yet in its 2009 letter to Mr Ban, Beijing appeared to be claiming sovereign rights over this second category of maritime areas in the South China Sea, contrary to Unclos.
Only predominantly island-nations, such as the Philippines and Indonesia, are recognised by Unclos as archipelagic states. Is China planning to become a latter-day archipelagic state based on its offshore island claims, by far the most extensive of which are in the South China Sea?
One thing is certain. China plans to reinforce its domestic law on its claimed maritime and offshore island rights. Xinhua reported on Dec 28 that China was likely to enact its first law on the exploration, development and management of deep sea resources within five years, as part of its policy to "resolutely safeguard maritime rights and build itself into a maritime power".
The writer is a visiting senior research fellow at the Institute of Southeast Asian Studies.