The name of the handler. There can be (should be) many handlers with the same name. The difference in how they function is the parameters to this rule and the matches captured from the pattern.
Parameters for this rule that dictate behaviour of the handler code.
A pattern for when to attempt to apply the handler code to the rule. The code may still refuse to handle the request so this is necessary but not sufficient.
A lookup for matching on the 'content' of a request - ie. request parameters. The key is the name of the parameter, and the result is an object with a regex pattern for the match.
A rule for handling an offline request. When this rule matches a request it is passed to the OfflineHandler registered with the handlerName, which then handles the request. Multiple rules may match the same handler.