Can you please explain how PHP execute this code and the result is true?
var_dump( (false < -1) ); //bool(true)
False is boolean type, and from PHP maunal:
-1 is considered TRUE, like any other non-zero (whether negative or positive) number!
Resource: http://php.net/bool
For comparison PHP is casting values to same types.
If -1 is casted to boolen, that is true, so if you compare false < true then true is correct value.