Our libraries contain all the POSIX and most of the common Unix function calls. Not only have we paid close attention to the POSIX standard but also to the de facto standards in the Unix community. The goal has been to minimize the pain in porting code.
However, we don't want to claim outright POSIX compliance because at this point we don't have the resources to dedicate to completing the implementation. We'd like to but, balancing that against our other priorities, full POSIX compliance will have to wait.