There
will be a proper rule-set (more like guidelines) soon™ though -- otherwise the most general notion has always been to use '
Common sense'.
The amount of variables applied to all the various issues that can spring up isn't something you can 100% set down a rule-set for, case in point the weapon rack.
For example:
Issues such as can you build a weapon rack, sure,
if you're not hurting your team by suicide 24/7 to do so. Common sense.
Can you use that weapon rack to spawn a lot of items to block paths with?
Obviously not.
Is it ok to build a weapon racks to create a archer/ranged spot?
It depends, but overall yes; As long as no one suicides on purpose to do so.
Also the fact that the rule regarding use of Weapon Racks have always been debated and subsequently changed back and forth. Either way, the Weapon Rack is the worst example you can find, and everyone who "gets in trouble" for either using/abusing it always knows that when using the weapon rack you're entering special territory, that much is a sure given when making the decision to use it, no one "just builds" a weapon rack for the benefit of the team.
Most administrative situations are based on variables and a lot of them, hence why we introduced the new
Ban Rules:
http://forum.melee.org/eu-(official)/ban-request-requirements-read-this-first!/There usually isn't a clear cut decision unless we're talking regular Team Kills or Team Damage issues, and even in those there often is more behind prompting us to check server logs for the full situation.