First, CSS is cascading, meaning a rule following another rule will override it. Second, attributes with an asterisk prepended to the property name are only picked up by IE7. Finally, in a nutshell, IE7 treats layout differently than other browsers. On IE7, certain elements get layout by default, but other elements can be "given" layout by using certain properties (that we refer to as "hacks") like `zoom: 1`. When an element has layout in IE7, it can be given a display of inline and act like inline-block. This is one of the many reasons why older versions of IE were such headaches for web designers. More info about IE7's hasLayout quirk can be found here[1].

If we apply what is described above into these rules, we get this:

1. display: inline-block is applied to the element.

2. on IE7, display: inline is added to the element.

3. on IE7, zoom: 1 gives the element layout, thus making it act like it act like an inline-block. Other browsers attempt to "zoom" the element, but since it's at "1", this is like saying "zoom the element 1x the size," so it does nothing.

I hope that helps clear up why we use this hack.

[1]: http://reference.sitepoint.com/css/haslayout

Not if you use it on the container itself, since it would apply to the interaction with floated elements that come before the one you use clear on - but here you open the container tag first, and then come the floats.

You could use clear on an element that comes after the floated elements, but before the container is closed, though. (you can also use the ::after pseudo element for this, maybe even in combination with ::last-child or something)