Unfortunately I don't think php works like that.
If you are changing $var4 you have to include $var2 and $var3 becuase they come before $var4 in the function declaration.
you could pass an array to the function with the default values and only change the $var4 value, or change the order as nickb suggested.
http://www.php.net/manual/en/functions.arguments.php#functions.arguments.default
Any way to specify optional parameter values in PHP?
