What are they and how do they work?
Legality challenges are the procedural mechanism by which players ask GenSec to rule on whether a proposal violates the Rules. A proposal is not a resolution. A resolution has been passed into law by the GA. A proposal is anything before the resolution passes.
To avoid the issue of proposals that break the rules passing into law, GenSec will scan the submission queue to ensure that no illegal proposals survive. However, what is illegal can vary based on interpretation, so often players will see something GenSec either misses or did not think was illegal in the first place. This triggers the process where GenSec will review the proposal.
This is distinct from the control panel rulings. You may notice that, when somebody submits a proposal, members of GenSec will mark it as Legal or Illegal. This is separate from the Legality Challenge system! Legality challenges are for relatively novel or complex issues of GA rules. Very nearly all Control Panel rulings are entirely administrative to keep the queue clean. Any others are so a submitted proposal does not reach vote before GenSec can deliberate.
After GenSec has accepted a Challenge, it will deliberate and issue a formal Decision or an informal ruling. Informal rulings occur when a challenge does not merit a full precedential decision, either because the challenger misunderstood a rule, missed some defining precedent, or because the challenger tried to challenge an illegal proposal still in the queue that would be addressed solely through the control panel. GenSec will usually explain the misunderstanding and decline the Challenge to avoid wasting time. We are concerned with formal Rulings.
Rulings, much like court opinions, lay out how GenSec decides a Challenge. Decisions require a majority of GenSec members available to agree. Decisions become precedential, or bind GenSec in the future. You may also see Dissents. Dissents occur when a member of GenSec disagrees with the ruling. For clarity, GenSec members who dissent must explain why so the players know it is not born of political animus or personal grudges. Dissents are not binding.
How do I make a challenge?
To make a challenge, one only needs to follow the Guidelines (https://forum.nationstates.net/viewtopic.php?f=9&t=401599):
Tag a new topic with [Legality Challenge] and the name of the challenged proposal and articulate your argument. Do not stop there! A good Challenge needs to be clear, concise, and accurate. A good challenger has already done their research and considered counterarguments. Most importantly, a good Challenge needs to clearly make it’s point. The best way to do this is to organize one’s writing.
One standard in presenting a clear written argument in the legal world is the IRAC system. IRAC stands for Issue/Rule/Application/Conclusion. It structures your arguments for ease of reading. A Legality Challenge will benefit from this considerably. To break it down, let us use an easy example of a proposal where the author misinterpreted a proposal, say GAR#10 Nuclear Arms Possession Act, as legalizing the unrestricted use of nuclear weapons. This is not a far-fetched misinterpretation, and will serve as a useful example. This is how it breaks down in IRAC:
Issue – This is your topic sentence, which embodies the point of your argument. In a challenge, you might write “Repeal: GAR#10 violates the Honest Mistake rule because the repeal does not address an argument specific to the target resolution.” This sums up your whole position. Easy!
Rule – This is a recitation of the rule in play. It may be the actual GA Rule, or it may be a legal rule that GenSec came up with to test. It need not be one sentence alone. For the Honest Mistake rule, you might use the following: “Repeal arguments must address the target resolution. See Honest Mistake Rule. Repeals must make a colorable interpretation of the target proposal to avoid making an Honest Mistake violation.  GAS 6.”
Here, you’ve made two rule statements. Initially, one based on the rule. This is a broad statement that does not entirely cover the issue at hand, so you follow it up with a narrower subset of the Honest Mistake rule. Now the reader knows what your point is and what rule is at issue.
This is the section where you put your citations. CITE YOUR SOURCES. GenSec can find its own rulings, but it much prefers it if you provide support for your claims. The details on what sources are persuasive and what are mandatory for GenSec is complicated, but generally: anything GenSec decided is binding. Anything the mods did is convincing but not dispositive.
Application – This is where the rubber hits the road. Application is where you apply your facts to the rule. Do not introduce new rules or issue into the mix here. An example of this might look like the following: “Repeal GAR#10 argues that NAPA permits unregulated nuclear weapon’s usage. However, the text limits itself solely to possession of nuclear weapons, not use. There is nothing in NAPA preventing the WA from regulating their use. The interpretation that it legalizes unrestricted use is therefore not colorable based on NAPA’s text.”
Conclusion – This is often a rehash of your topic sentence. Its where you make your final point. It seems repetitive, it is both logically complete and rhetorically helpful to add the Conclusion line. For our example this may look like: “As such, the repeal violates the Honest Mistake rule and is illegal.” And you are done!
When Not to make a Challenge:
You know how to make a challenge. The harder lesson: When NOT to make a challenge.
Legality challenges are taxing on GenSec. They are often under a deadline to decide a technical question that demands complex consideration while also balancing real life demands. Imagine doing your job all day and then having to come home and do it for free!
Frivolous or unnecessary Challenges also hurt the game: the GA has a very steep learning curve, but when you throw unnecessary Challenges and legality battles into the mix, you set the mood from challenging task to ordeal. Before you file a challenge, run through the following questions:
Is it too early in the drafting stage?
Many players will draft for weeks or months. If a draft has a legality issue that can be addressed with a limited edit, discourse rather than a challenge is the best approach. If the player is intransigent, consider filing a challenge only as the draft nears submission.
Is the illegality very minor?
This is not to say that small violations are acceptable, but that a Challenge hinges on a tenuous reading. If you think you might be wrong, its more likely than not that your theory is probably not that strong. Remember: Challenged proposals get a lot of leeway to keep the game accessible. If you must squint and look at the issue sideways to see it, it is probably not a strong argument.
Is the illegality extremely obvious?
GenSec will get the obvious ones. GenSec members really do not need to worry about a Challenge against a Repeal of GAR#1, since they will just nuke it with the control panel.
Is the proposal at vote?
This is less a question of whether your challenge is warranted but of practicality: The closer to passing an at-vote proposal is, the less happy GenSec will be about dealing with the Challenge. The timeframe is short, even for a Challenge, and people often already sent campaigns. 11th-hour challenges draw a great deal of skepticism, especially if you were active in the thread already. There is also a greater chance that players have seen the illegality and that it was addressed. Try to keep separate your political arguments and your legal arguments! The Rules are there to make the game manageable, not to squash political enemies when they are ahead.
Is your interpretation against the intent of the rules?
The Rules exist to benefit the game as a whole and are applied in a way that lets GenSec address problems in the game and not as literal gospel. While GenSec takes great steps to keep their power and influence constrained for predictability, Gotchya! arguments that have a net negative influence on how the game works usually will not fly. A great (but long-resolved) example is the claim that Honest Mistakes only apply to accidents, not intentional lies. While the rule may not clearly address lies, everybody in the GA can see that allowing lies in repeals will make the game a miserable mess and not a fun experience.
Remember, these are rules of thumb, not hard rules. Consider them before you make a challenge, but do not let them stop you if you see a real issue.