Read the value of a class constant.

This is the same as just typing self::CONSTANTNAME, but throws a more useful message if the constant is not defined and allows the constant to be limited to a maximum length.

Return true if this rule can be applied to the given object.

Some policy rules may only operation on certain kinds of objects. For example, a "task author" rule can only operate on tasks.

Return true if the given value creates a rule with a meaningful effect. An example of a rule with no meaningful effect is a "users" rule with no users specified.

Tell policy rules about upcoming transaction effects.

Before transaction effects are applied, we try to stop users from making edits which will lock them out of objects. We can't do this perfectly, since they can set a policy to "the moon is full" moments before it wanes, but we try to prevent as many mistakes as possible.

Some policy rules depend on complex checks against object state which we can't set up ahead of time. For example, subscriptions require database writes.

In cases like this, instead of doing writes, you can pass a hint about an object to a policy rule. The rule can then look for hints and use them in rendering a verdict about whether the user will be able to see the object or not after applying the policy change.

Return a unique string like "maniphest.author" to expose this rule as an object policy.

Object policy rules, like "Task Author", are more advanced than basic policy rules (like "All Users") but not as powerful as custom rules.