Do double forward slashes direct IE to use specific css?

Question

I have just found something very weird while developing a website. While trying to get a div element to display across the top of the screen, I noticed that I wasn\'t achiev

Answer 1

// is not a valid CSS comment.

Browsers that parse CSS properly will ignore //position because //position is not a valid property name (details are here, property -> IDENT S* -> follow it through).

This only works in IE7 due to its well known bug of accepting properties with junk prepended to them.

It's not just // that works. IE7 will have red text here:

body {
    !/!*//color: red;
}

This is most typically exploited with *, for example *display: inline; as part of the display: inline-block workaround for IE7.