If any of these bits set, a symbolic debugging entry

Only symbolic debugging entries have some of the N_STAB bits set and if any of these bits are set then it is a symbolic debugging entry (a stab). In which case then the values of the n_type field (the entire field) are given in <mach-o/stab.h>

Private external symbol bit

Mask for the type bits

External symbol bit, set for external symbols