MinecraftForge/common/net/minecraftforge/event/EventPriority.java

package net.minecraftforge.event;

public enum EventPriority
{
    /*Priority of event listeners, listeners will be sorted with respect to this priority level.
     * 
     * Note:
     *   Due to using a ArrayList in the ListenerList,
     *   these need to stay in a contiguous index starting at 0. {Default ordinal} 
     */
    HIGHEST, //First to execute
    HIGH,
    NORMAL,
    LOW,
    LOWEST //Last to execute
}