… macro definition
The footnote claiming that reading the fd_set takes time proportional to the number of fds is confusing, since both the sentence referencing that footnote and the example right above that sentence are saying that the time is proportional to the largest fd. Of course it's possible to do better by storing the fds separately, but the footnote should not imply that this was done here.
The doxygen correctly described its allowed values as 1/0, but we were saying here that it took true/false.
… quite often.