Available on Sys
@:value(cast 0)@:impl@:enuminlineread onlyClose:MessageCommand = 0
@:value(cast 1)@:impl@:enuminlineread onlyData:MessageCommand = 1
@:value(cast 2)@:impl@:enuminlineread onlyExit:MessageCommand = 2
@:value(cast 3)@:impl@:enuminlineread onlyStart:MessageCommand = 3