So the user agent can be faked.. Ok… is there a valid reason why I shouldn't use php to detect the browser?

Question

I have never understood why some people say making custom css for each browser is a bad thing. To keep my page size down and download times fast it makes perfect sense to me to make a custom css for the major browsers (especially IE in its many different forms), and a general catch all css for everything else.

If you want to send out a bloated, huge, Swiss army knife of the css world, for all situations then go right ahead I'm not going to stop you.

Fast detection of the browser is important when doing this. Loading a JavaScript file to detect the browser seems slow. So I would prefer to use php to detect the browser, and send out the specified css. Or at least a general browser specific css then use the JavaScript to load a more detailed version of the css.

But I've read article after article about why this is a bad thing. The main reason behind each of these articles is because the user agent can be faked. Or there using Firefox but the server thinks they're using IE7 so it sends out the wrong css file.

As a developer/designer of web apps why is this my problem? If you want to use Firefox, but tell my server your using safari or IE*, and get a crappy looking page, why is it my problem?

And don't throw that whole if the user can't see your site right they'll never come back, or some kind of similar argument at me. a normal user isn't going to be doing this. its only going to be the people who know how to do this, and will know whats wrong when my site looks crappy.

This is similar to looking at my site on a old Apple II (I have no clue how), and yelling at me because everything looks green.

So is there a good reason, not a personal preference, why I shouldn't use php to detect the browser and send out customized css files?

I do this mostly for the different versions of IE. It just seems like for some sites, adding the if IE6 and if IE7 parts just double or triple the size of the css file.

Answer 1

As long as the only thing you're doing is changing style sheets, there is no valid reason as far as I can tell. If you're attempting to deliver custom security measures by browser, then you'll have issues.

Answer 2

Typically when a user intentionally fakes the user agent string, it is because something is not viewable in the user's browser that should be. For example, some sites may restrict users to IE or Firefox, but the user is using Iceweasel on Debian. Iceweasel is just a Firefox renamed for trademarked reasons (there are a few other changes also), so there is no reason that the site should not work.

Realize that this happens because of (bad) browser detection, not despite it. I would say you don't need to be terribly concerned about this issue. Further, if you can just make your site reasonably cross-browser compatible, it won't matter at all. If you really want to use browser-specific CSS, and you don't want to do so all in one CSS file, don't let a fake user agent stop you.

Answer 3

Not sure about php but in Rails it is normal and dead simple practice to provide css files and different layouts based on the user agent particularly when considering that your site is just as likely to be accessed by any of the myriad of available mobile devices, never mind writing for the most popular (Currently Firefox) browsers and even writing custom MIME types if need be is also dead simple.

IMO not doing so is pure laziness on the coders part but then not all sites are developed by professional teams of developers with styling gurus at hand. Also in languages other than Rails it might not be so simple. Sorry, I haven't a clue about PHP so this may not be an appropriate reply

Answer 4

In my opinion, starting with normalize.css, and having a base style sheet to start, overriding the base styles as needed usually works along with making sure you set appropriate fallbacks. If you really need it a few media queries, and feature detection can go a long way.

Answer 5

One reason you shouldn't base things off of the browser is because major search engines like Google and Yahoo prohibit displaying different content for different browsers. GoogleBot can detect different CSS and HTML and you may get bad search positioning. Additionally, if you use any advertising services you may be in breach of their contract by displaying varying content.