provided, that is how many messages can be stored in the thread's mailbox before blocking senders. The capacity must be between 1 and 65535 inclusive, and defaults to 10. Can optionally provide flags to the new thread - supported flags are:

* :h - Start a heavyweight thread. This loads the core environment by default, so may use more memory initially. Messages may compress better, though.

* :a - Allow sending over registered abstract types to the new thread

* :c - Send over cfunction information to the n