auxiliaryData: pointer to 4 integers. auxiliaryData should be a unique identifier different from 0. Use a large random identifier, or better, your CoppeliaSim serial number if the message is yours. Otherwise, use the identifier of some other module. auxiliaryData could be the messageID of the message you wish to send to another module. auxiliaryData and auxiliaryData can be any values specific to your application.
customData: customData of your application (the broadcaster is in charge to release that buffer). Can be nullptr.
replyData: pointer to 4 integers that can be used by a module to reply to a broadcasted message. Can be nullptr. If not nullptr, all 4 values are automatically initialized to -1.
Broadcasted messages can be intercepted in a plugin's "simMessage"-function.