Supported CSS hacks

Most style sheets will contain one or more "hacks"; uncommon arrangements of CSS which exploit features or errors in the parsing code of some browsers. These are used to target individual properties or rule sets at specific browsers. The most common types, which are unfortunately invalid CSS, are the 'star' and 'underscore' hacks. Support for these and some Internet Explorer-specific CSS properties are included in cssprepare by default as they are so prevalent, but it can be turned off with -h (--disable-hacks).

star hack

Any property preceded by an asterisk (eg. *width: 100px;) is ignored as an invalid property by every browser, except Internet Explorer versions 7 and earlier.

underscore hack

Any property preceded by an underscore (eg. _width: 100px;) is ignored as an invalid property by every browser, except Internet Explorer versions 6 and earlier.

IE-only properties

There are a couple of invalid properties that cssprepare will accept when hack support is enabled, but only if they are combined with either the star or underscore hack.

They must be combined with a hack because, starting with Internet Explorer version 8, these properties have been corrected to require the -ms vendor extension in order to work. Microsoft are stating that the earlier behaviour was incorrect, so they should be demarcated with an IE-targetting hack.

zoom

zoom: 1; is commonly used to trigger the hasLayout property in Internet Explorer (which fixes many common rendering issues).

filter

The filter property is commonly used to implement effects such as gradient fills and PNG support.