Making the cache directory writable by PHP

[e2xperimental]

Regarding step 4, "Your cache directory of choice must be writable by PHP"...

How do you make the cache directory writable by PHP without making it world writable drwxrwxrwx?

For security reasons, we don't allow world writable folders to be accessible to everyone via the web.

I tried restricting the folder's permissions slightly drwxrwxr-x but the debugger returns this:
tweet.js: Cache directory is not writable jquery.tweet.js:277