Both the $myVar assignment in line 1 and the $higher assignment in line 2
are dead. The first because $myVar is never used and the second because
$higher is always overwritten for every possible time line.
The variable $data does not exist. Did you forget to declare it?
This check marks access to variables or properties that have not been declared yet. While PHP
has no explicit notion of declaring a variable, accessing it before a value is assigned
to it is most likely a bug.
This check looks from parameters that have been defined for a function or method, but which are not used in the method body.