php startsWith, endWith

startsWith("abcdef", "ab") -> true 

startsWith("abcdef", "cd") -> false

startsWith("abcdef", "ef") -> false

 startsWith("abcdef", "") -> true 

startsWith("", "abcdef") -> false 

endsWith("abcdef", "ab") -> false 

endsWith("abcdef", "cd") -> false 

endsWith("abcdef", "ef") -> true 

endsWith("abcdef", "") -> true 

endsWith("", "abcdef") -> false