A couple of comments by Maori Party co-leader Tariana Turia about the Marine and Coastal Area (Takutai Moana) Bill are hardly reassuring. The first reserved the right of Maori to try to change the legislation at some unspecified future date.

Secondly, in a Perspectives article in this newspaper, she said that only "time will tell how all of this [iwi and hapu claims for customary title] will pan out in the courtrooms or in direct negotiations with the Government".

Both comments indicated a lack of certainty about the legislation, much of which relates to its lack of explicitness. It is a shortcoming that should be repaired as far as possible in the bill's select committee stage.

All legislation is, of course, subject to change as circumstances alter. Perhaps Mrs Turia felt obliged to make that point because of the stand taken against the bill by Hone Harawira, one of the Maori Party's own MPs.

Nonetheless, it is alarming to hear such a view so soon after the first reading. It is not exactly a ringing endorsement. Her viewpoint will particularly irritate those who have put an immense amount of effort into finding a way to rectify Maori grievances over the 2004 Foreshore and Seabed Act.

Mrs Turia's talk about the uncertainty over the outcome of customary title claims was more understandable. This country's legal system sees Parliament and the courts as co-generators and co-administrators in the rule of law.

What Mrs Turia is suggesting is that shortcomings in specificity mean the courts will play an especially significant role in how this bill pans out. That creates a heightened level of doubt which is not especially helpful.

Two examples are obvious. One involves the condition that to qualify for customary title, a hapu or iwi must demonstrate it has exclusively used and occupied a specified area from 1840 onwards without substantial interruption. No definition of "exclusivity" is offered in the bill.

The Attorney-General says it is a common law concept which requires an applicant to show its interest in an area was akin to ownership in that it was able to exclude non-members. But what, for example, if iwi had allowed others to use a beach, rather than actively excluding them? Does this disqualify a claim?

Also, the bill does not spell out that access to a beach must be free if it is held in customary title. The Attorney-General made a point of telling Parliament there would be no charging for access, thereby alerting the courts to the bill's intentions. But if this is so, why is it not stipulated? At the very least, it has given the bill's opponents something on which to seize.

Mr Harawira's complaints are more fundamental. He says little will change because the threshold that hapu and iwi have to meet to gain customary title is too high.

That problem is exacerbated, he says, by the Crown having the resources and ability to fight in court. Mr Harawira is right that the threshold is high, although the courts are set to have a big say in that. But the bill does go to some lengths to help Maori applicants.

First, the burden of proof in seeking or opposing customary title will fall equally between the claimant and the Crown. Secondly, the Attorney-General has indicated that Maori preparing an application are likely to get funding for historical research. Court costs can also be avoided if an iwi chooses to negotiate directly with the Crown.

Mr Harawira concedes the bill achieves two of the Maori Party's aims: the repealing of the Foreshore and Seabed Act and the restoration of the right to contest ownership in court.

The latter looms large in the equation. The legislation will be all the better if it emerges from the Maori affairs select committee as a more definitive document.