meaning PJ_DEF in function definition

[maternick@xxxxx (mk)]

Hi
I would like to know what means PJ_DEF in some functions definitions e.g.
PJ_DEF(const char *) pjsip_tsx_state_str(pjsip_tsx_state_e state)
{
     return state_str[state];
  }
, beacuse I have problem with generating tags by ctags-execuberan on these  
functions.

Regards, Michal