Express.js checking request type with .is() doesn't work

I'm trying to check what the type of content is, but it doesn't appear to be working. Here is the output on the shell:

$ node app.js
# Request http://localhost:3000 via browser
CLIENT DOES NOT WANT XML, JSON, OR HTML
text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8

And here is the contents of the app.js script:

var express = require('express');
var app = express.createServer();

app.get('/', function(req, res) {
    if (req.is('xml')) {
        console.log("CLIENT WANTS XML");
    } else if (req.is('json') || req.is('html')) {
        console.log("CLIENT WANTS JSON OR HTML");
    } else {
        console.log("CLIENT DOES NOT WANT XML, JSON, OR HTML");
        console.log(req.header('Accept'));
    }
});

app.listen(3000);

I would expect the text/html Accept header to trigger the req.is('html') function or even the application/xhtml+xml Accept header to trigger the req.is('xml'), but the else statement actually gets run. I'm using Express 3.0.0 rc1 and Node 0.8.1.