forward slash in CSS? Is this some browser specific thing?

I inherited a CSS stylesheet and in a few places it does things like:

margin:7px 0 0 0;
/margin-top:9px;

or

background: url(../images/list-hover.png) 0 0 no-repeat;
/background:url(../images/lists-hover.png) 0 2px no-repeat;

anyone know what that forward slash is doing?