I need to run a set of RewriteCond statements if an ENV is true or defined (if not defined, then presumed false). I've been trying to use:

```
RewriteCond %{ENV:IS_MOBILE} ^true$
RewriteCond ...

```

and (not sure if this is even valid)

```
RewriteCond %{ENV:IS_MOBILE} !=true
RewriteCond...

```

But neither seem to work. Any way I can do this?