Code:
div {
width: 100px;
}
div {
\width: 140px;
w\idth: 100px;
}
The top rule (line 1) is used by browsers like Op5 that get the box model correct, but choke on the escapes in the following rule. Op5 ignores those rules entirely.
The first 'escaped' property (line 5) will be used by IE5.x, and feeds that browser its 'fudged' value. The second escaped property (line 6) cannot be read by IE5.x, but is read and used by modern 'escape friendly' browsers like N6, Moz, Op6, and IE6.
Note: If Nav4 sees even one escape anywhere in the CSS, it will discard the entire sheet. So it is vital that this hack be hidden from that browser, by means of @import, or the CaioHack. For a detailed explanation of the escape parsing bug see that Andrew Clover [post].
Proper use of the escapes: The escape '\' that starts line 5 must always be directly against the first letter of the property name. IE5.x/win does not like escapes, but seems to ignore them when they are in this position.
Important! An escape must not precede any of the first six alphabetical characters: a, b, c, d, e, f, per the [CSS spec on forward-compatible parsing]. If this is done it will be seen as a 'hex code' and Bad Things Will Happen. This means that a property that begins with one of these letters cannot be hacked in this manner. For example, "height" can be hacked, but "font-family" can't be, since it starts with a character that is interpreted as the beginning of a hex code. Fortunately, neither "width" nor "height", the most important properties for this hack, are affected.
For line 6 (modern browsers) the escape must be within the property name, and the previous 'hex' rule applies.
Check voor alle hacks:
http://css-discuss.incutio.com/?page=BoxModelHack