Have you read the Senate's bipartisan immigration-reform framework yet? At four pages, it's a quick and clear read. But because it's only four pages, quite a bit is left unsaid, or undefined. So here's what you should keep a particularly close eye on:

1) "Contingent upon our success in securing our borders and addressing visa overstays."

The key word in the framework is "contingent." Everything is contingent upon the securing of our borders. But how will we known when our borders are secure? "Our legislation will create a commission comprised of governors, attorneys general, and community leaders living along the Southwest border to monitor the progress of securing our border and to make a recommendation regarding when the bill’s security measures outlined in the legislation are completed."

As Greg Sargent writes, "The fate of immigration reform, then, largely rests on what this commission looks like, who is on it, and what metric it uses to decide when the border is secure."

2) "Our legislation also recognizes that the circumstances and the conduct of people without lawful status are not the same, and cannot be addressed identically."

There's a lot you have to do to qualify for the path to citizenship in this bill. "Go to the back of the line of prospective immigrants, pass an additional background check, pay taxes, learn English and civics, demonstrate a history of work in the United States, and current employment, among other requirements."

But that's not true for everyone. The framework makes clear that the law won't treat all undocumented immigrants identically. The obvious exception is children, and sure enough, they get a special mention: "individuals who entered the United States as minor children did not knowingly choose to violate any immigration laws. Consequently, under our proposal these individuals will not face the same requirements as other individuals in order to earn a path to citizenship."

The more unexpected exemption is agricultural workers. "Individuals who have been working without legal status in the United States agricultural industry have been performing very important and difficult work to maintain America’s food supply while earning subsistence wages. Due to the utmost importance in our nation maintaining the safety of its food supply, agricultural workers who commit to the long term stability of our nation’s agricultural industries will be treated differently than the rest of the undocumented population."

3) "Our new immigration system must be more focused on recognizing the important characteristics which will help build the American economy and strengthen American families."

Perhaps the key architectural question in building a new immigration system (as opposed to figuring out what to do with the failures of the last immigration system) is deciding whether we'll focus our visas on drawing needed skills (for instance, by favoring immigrants with advanced degrees or who work in sectors, like agriculture, where we need more labor), emphasizing family unification or something else.

This paper mentions both family reunification and skills. And to some degree, that's fine: We don't need to choose simply one or the other. But since we're not moving to an open-border policy, the fact that we're offering a limited number of visas will mean that we have to choose how many of them go toward  reuniting families and how many go toward filling our perceived economic needs. Those ratios are left undefined in this framework, but they'll be one of the most hotly contested elements of the actual law.

4) "Our immigration proposal will award a green card to immigrants who have received a PhD or Master’s degree in science, technology, engineering  or math from an American university."

Remember when Mitt Romney said, "If the [immigrant] student does so well that they get an advanced degree, I'd staple the green card to their diploma"? This law basically does that.

5) "Our proposal will provide businesses with the ability to hire lower-skilled workers in a timely manner when Americans are unavailable or unwilling to fill those jobs."

This refers to some kind of guest worker program, though the details are sparse and the language is vague. The section mostly focuses on the hoops employers would have to jump through, including demonstrating "that they were unsuccessful in recruiting an American to fill an open position and the hiring of an immigrant will not displace American workers." But guest-worker programs are always controversial, and how big this program is, how difficult the qualifications are, who qualifies, etc., are all left unresolved in this paper.

As just one example, consider the complexities in implementing this sentence, which is all the paper says about how to move out of the guest worker program and into green-card status: "Permit workers who have succeeded in the workplace and contributed to their communities over many years to earn green cards."