In a pure OOCSS style of writing CSS, let's imagine you created a css class of .button that visually turns a simple link into a button.
<a href="#" class="button">I'm a button</a>Now, if you want to define a custom version of your button, let's say a button that will trigger a very dangerous action, you might want to style it differently, so our user will think twice before hitting it.
You got two ways of achieving this, depending if you still support IE6 or not.
Simple way for non-IE6
If you don't care about IE6 (and hell, it's 2012, you shouldn't), you just have to add a second class to your button/link :
<a href="#" class="button dangerous">I'm a dangerous button</a>
And in your CSS file, just define some special styles (like a red background) to your dangerous button.
.button.dangerous { ... }Actually, that's the path followed by Bootstrap (among others). But it will not correctly work in IE6, because it does not understand multiple classes rules. Instead, IE6 will read .button.dangerous {} the same as .dangerous {}.
This will cause problems as soon as you'll use the .important class on something else than a .button : IE will apply the .button.dangerous rules to anything with the .dangerous class.
Other way, for IE6
The solution I personnaly use to fix IE6 is to use more explicit classes instead of using multiple ones. For example, instead of .button.dangerous {} I'll use .buttonDangerous {} and write my html like this :
<a href="#" class="button buttonDangerous">I'm a dangerous button, even on IE6</a>
That way, the link will have both the styles of .button and .buttonDangerous. This will assure cross compatibility with IE6, at the expense of a (arguably) less readable markup.
As of today, I hope that I'll never have to code for IE6 websites again, but if you ever need to, that's a little trick that can really help.
