I'm truing to parse arguments like http://localhost/img/
module/border.php?type,colorScheme,template.
How to parse it by $_GET?
print_r($_GET); outputs Array ( [type,colorScheme,template] => )
What you wrote in $_GET is 1 variable.
To separate multiple $_GET variables, use &.
http://localhost/img/module/border.php?type&colorScheme&template
To assign values write
?type=sometype&colorScheme=somecolor&template=sometemplate
If you really need/want to send 1 $_GETvariable as you wrote, use explode() which need the delimiter and the string to split:
explode(",", key($_GET));
Array ( [type,colorScheme,template] => )" ... well, yes ... that's what you've sent - what were you expecting?key().