function callExpression( node ) {
		var alias;
		var arg;
		var id;

		if ( isNamespaceAssignment( node ) === false ) {
			return;
		}
		if ( node.arguments.length ) {
			arg = node.arguments[ 1 ];
			if ( arg && arg.type === 'Literal' ) {
				alias = arg.value;
				debug( 'Namespace property: %s', alias );
			}
			arg = node.arguments[ 2 ];
			if (
				arg &&
				arg.type === 'CallExpression' &&
				arg.callee.type === 'Identifier' &&
				arg.callee.name === 'require'
			) {
				id = arg.arguments[ 0 ].value;
				debug( 'Package identifer: %s', id );
			}
			if ( alias && id ) {
				debug( 'Found a namespace assignment.' );
				out.push({
					'id': id,
					'alias': alias
				});
			}
		}
	}
Callback invoked upon visiting a `CallExpression` AST node.

@private
@param {Node} node - AST node
@param {*} state - start state
@param {Callback} clbk - callback to continue walking a sub-node