The Old Code

The Old Code is a set of a widely accepted forms of courtesy and terms of engagement, establishing procedures for things such as hostage exchanges, negotiations, rites of passage, neutral territories, laws of hospitality, trade, neutrality and other such things.
The Code is known to most scholars and most organizations and cultures across the realms follow the terms outlined in it to one degree or another when interacting with each-other or with outsiders.
The Old Code can be summed up in one sentence: Keep to your agreements and behave honourably.

Breaking the Code

Breaking the Old Code once it is invoked is generally a bad idea. The code is enforced by several owerful factions across the brass realms as well as most cultures. However the primary enforcers of the Old Code are the Fateweavers. They ensure that any outrageuous and public breaches in the old code are swiftly followed by bad luck and catastrophy for the offenders.

More indirectly, those that break the code openly show themselves as untrustworthy, and social ostracization and attacks by their enemies are sure to swiftly follow any breach. And while transgressors may not be fought openly by their allies or neutral groups, they will also not be helped (at least not publicly).
Despite this, parties try and succeed in breaking the Old Code all the time, and though it usually has negative consequences for the offending party if discovered, many still attempt it and many get away with it by following one simple rule; Just dont get caught.

Established Procedures:

The Old Code establishes the following:

Neutral Arbiters & Territories

Neutral Arbiters: Neutral parties are those that agree to arbitrate in case two parties wish to have a neutral party to cast judgement or oversee an exchange. How 'neutral' these parties are can vary greatly. The most famous neutral party are perhaps the Mechanoids that arbitrate conflicts brought to them in Ezria.

Neutral Territories: Neutral territories are spaces chosen for trade or discussion by the participating parties. If the chosen space is claimed by a third party, that party will be responsible for enforcing its neutrality and preventing and punishng any violence during the exchange.

Duels

To resolve any conflict, often with lesser casualties than open warfare, duels are a very useful method.
The accuser can challenge an accused to a duel, for any reason. If the accused refuses the duel, then it won't happen.
If both parties agree to duel, both must select a 'second', who will assist to negotiate the terms of the duel and observe the results.
The conflict is overseen by a neutral party which is chosen by both the accuser and the accused (or their respective second).
The accuser selects the time and place, the accused selects the weapon/test/contest from a list of options. The neutral party decides what options are on the list the accused chooses from, and wether the chosen location is adequate. If the parties involved cannot agree on the terms of the duel it will not happen.
After the duel, the neutral party will declare the results and the seconds will attest to its veracity. The stakes of the duel must then be enacted.

Laws of Hospitality

Hosts: If somebody has promised safe passage or a safe stay under the Old Code, they are obligated to not harm their 'guest' and to protect them in case a foreign entity attempts to harm them. They are expected to provide food and lodging, if the guest requires it and they are capable of providing such. All of this only applies if the guest also behaves as a proper guest.

Guests: If a person promises to behave themselves as a guest should under the Old Code, they are obligated to respect the host's customs. They are not to harm the host, their property or any under their protection while they stay inside their domain. They are obligated to not abuse their host's generosity and not cause them undue trouble. They are obligated to leave if the host asks them to do so. All of this only applies if the Host acts as a proper host.

Warfare

In Warfare, almost anything is allowed. With the wide range of species, tricks, tactics and methods of warfare across the realms, anything too restrictive would just never be followed and thus pointless. However some methods are enforced by the arbiters of the Od Code as effective.
Declarations Any large-scale conflict should be precedet by a declaration of war. The larger the organizations involved, and the shorter the interval before initiation of conflicts, the higher the risk of bad fortune for the attacker. Its best to be courteous where possible.
Terms of Warfare If the two conflicting parties are fighting within an established ruleset, such as for example a ritualistic or religious war, then terms can be outlined upon war declaration and those that break the terms shall be punished.
False surrenders To falsely surrender and take advantage of legal loopholes or your opponent's mercy will swiftly earn you not only their ire but also the consequences of breaking the code, if you are caught doing so.

Signatories

The Old Code is backed and supported by several parties that have a vested interest in its maintenance. These parties include:
The Divine Machine
The One Above All
The One Below All
The Church of Haven
The Fates
The Fairy Queens
And many more