真的需要* html选择器吗？

Question

I just read this code somewhere.

*html #menu ul{margin: 0px 0px 0px 40px;width:960px;}

I know * means the selector means any element in css. But is this needed here? Since it works totally the same without it.Or is it some kind of CSS hacks in specific browsers ?

Answer 1

It is a CSS hack targeted at Internet Explorer 6 and below. More modern browsers should ignore any of the styles applied using *html .

List of browsers which will apply the styles

• IE4-6/Win
• IE4-5/Mac
• IE7+, when in backwards compatibility mode (aka quirks mode)

List of browsers which will ignore the styles

• IE7+, when in Standards Compatibility mode
• Firefox
• NS6.0-7.2
• NS4.x
• Opera 5+ (I don't know about versions 1 through 4.)
• Safari
• Konqueror 3
• iCab 3

Source: * html ("Star HTML") CSS Hack

So, provided your document is valid then IE7+ should display the page in standards mode and will ignore the styles. If the page is being displayed in 'quirks mode' then the styles will be applied in IE7+.

Answer 2

The Star Selector Hack

The star selector hack, also known as the star-HTML hack and the Tan hack, because it was first described in detail by Edwardson Tan, is the most widely used filter; it relies on a peculiar behavior in Internet Explorer 5.5 and 6. Even though it's often labeled a hack, I've included it in this section on filters because, despite the fact that it exploits a browser bug, it uses a valid CSS selector. The selector, however, should never match any elements; all browsers, except Internet Explorer 5.5 and 6, understand this fact and ignore the rule.

The technique is simply to apply a descendant selector that makes use of the universal selector. The universal selector is, of course, valid CSS, so don't be confused and start thinking that using the universal selector is bad news. The most common form of the technique (and the origin of its name) is to compose a rule with the * html selector. This constitutes valid CSS, but it shouldn't match any elements. The selector should apply the rule to any html element that's the descendant of any other element and, as html is the root element, it's never a descendant of any other element.

However, while most other browsers ignore it, Internet Explorer 5.5 and 6 will interpret this selector as if there was no universal selector, like the rule below:

html {
  ⋮ declarations
}

Thus, the star selector hack is a safe way of applying CSS rules to Internet Explorer 5.5 and 6 without affecting other browsers.

You'd use it like this:

.test {
  position: fixed;
}
* html .test{
  position: absolute;
}

Only Internet Explorer 6 and earlier versions will apply the latter rule; other browsers will ignore it.

Source : http://reference.sitepoint.com/css/workaroundsfilters#workaroundsfilters__sect_starhtmlselector