As far as I know, ENIGMA doesn't seem to support making constants, yet. I tried some methods, but the only one that worked was "global.variable = value".
And yeah, that space _ thing I said before deleting my post (lol).
It is possible to use constants, but it's very tricky to find how to do it !
Constants can be declared with an enumeration. For example :
enum { RIGHT, LEFT, DOWN, UP };
But the problem is that if you declare an enum in a script or in an object, you get an error message (c.f :
http://enigma-dev.org/forums/index.php?topic=1917.0). But if you go to ENIGMA settings, and you go to the 'Definitions' section, and you put the enum there, it works ! The only problem is that ENIGMA settings are global for every project, so be careful to update these settings if you load another project or you make a new project, because by default these settings will not change.