The FKM clear key's primary role is to remove the trigger made by the FKM keys. That is when a matching "clearKey" is detected alongside the partnering FKM keys.
Say we have the word "error" as the fail key and the word "clear" as the clear key.
Scenario 1: fail key was keyed in the log file and then the sampling ran, and just a few seconds the clear key was inputted and then the second sampling ran.
Scenario 2: Fail key entered on the first line and then the clear key entered on another line but were both detected within the same sampling period.
Scenario 3: Fail key and clear key are on the same line of the monitored log file.
P.S Note that the clearKey by default operates on "latest" mode, which explained as "The latest matching trigger row is cleared by the clear key"
For more info, check the FKM Plug-in User Guide and Technical Reference manual