Howto change DoubleClick-behavior in mousepad?

[PC-vor-Ort, Marcus Orthbandt]

I'm writing many PHP-Codelines with mousepad on Debian with XFCE.

Code-Sample:
$test=1+5;
echo $test;

If I do a doubleclick on "test", "test" will be marked/selected. Ok.
But for me should it be better to mark "$test" at doubleclick on "test".

For the application xterm I can change the charClass in .Xresources to 
manage the behavior an doubleClick.

Has anyone any hint, how i can change doubleClick behavior at mousepad 
or geany?
Who controll this behavior? The application (mousepad) or GTK or XORG?
Which config options can I test?

Thank you!