Where can I find the DEFINITION of vibe IOMode ??

[Andy Balba via Digitalmars-d-learn]

Where do I fine where IOMode is defined..  as in the last line of 
...

module vibe.core.stream;
import vibe.internal.traits : checkInterfaceConformance, 
validateInterfaceConformance;
import vibe.internal.interfaceproxy;
import core.time;
import std.algorithm;
import std.conv;

public import eventcore.driver : IOMode;

After endless searches, I find many references to it, but never a 
DEFINITION of it