Evfilter library documentation
 This filter implements barrier that holds events until sync event comes. This is especially usefull when routing several sources of input events so that they are not mixed up.
history  | 
unsigned integer  | 
Maximal number of events in queue.  | 
This filter writes human readable decomposition of event into file (or stdout or strerr). It’s usefull for debuging.
prefix  | 
string  | 
Prefix for all lines  | 
file  | 
path  | 
Path to a file, stdout and stderr are special  | 
This filter removes all key repeat events.