According to https://mandoc.bsd.lv/mdoc/style/function_pointers.html.
before:
SYNOPSIS #include <sys/types.h> #include <sys/sbuf.h> typedef int ( sbuf_drain_func) ( void *arg, const char *data, int len); ...
after:
SYNOPSIS #include <sys/types.h> #include <sys/sbuf.h> typedef int (*sbuf_drain_func)(void *arg, const char *data, int len); ...