How to specify which Require.js modules are compressed with the optimizer and which are not?

Using the Require.js optimizer with Node.js, I only want to compress some of my project files. How do I specify which files I want compressed? This is my current node.js script:

var requirejs = require('requirejs');

var config = {
baseUrl: '/common',
name: 'main',
out: '/compressed'
};

requirejs.optimize(config, function (buildResponse) {
//buildResponse is just a text output of the modules
//included. Load the built file for the contents.
//Use config.out to get the optimized file contents.
var contents = fs.readFileSync(config.out, 'utf8');
});

I just want to compress the files in common. Main is also in common. There are files outside of common that are dependencies that I do not want to compress. How does the optimizer choose what files to combine?