How does the MaxConcurrentExecutables parameter in SSIS affect parallel processing of packages?

The MaxConcurrentExecutables package property when set to -1 means the maximum number of concurrent executables equates to the number physical or logical processors plus 2. For example 8 processors plus 2 = 10, therefore MaxConcurrentExecutables will be 10 Does this mean the MaxConcurrentExecutables across all packages that happen to be running at the same time is 10, or is it actually 10 per package? For example, two separate packages running at the same time can each run a max of 10 each, or is it a max of 10 concurrently for the whole SSIS server?