css - css coding that I have never seen

Question

I am studying a free css template called zerofour found at http://html5up.net/zerofour/, and running across a css coding that I have never seen before. In the HTML, some divs have class such as "4u", but when I check the css files, this is the only text section that has anything with those terms, and it looks like this:

/* Grid */

/* Cells */

    .31 2u { width: 100% }
    .31 1u { width: 91.6666666667% }
    .31 0u { width: 83.3333333333% }
    .39 u { width: 75% }
    .38 u { width: 66.6666666667% }
    .37 u { width: 58.3333333333% }
    .36 u { width: 50% }
    .35 u { width: 41.6666666667% }
    .34 u { width: 33.3333333333% }
    .33 u { width: 25% }
    .32 u { width: 16.6666666667% }
    .31 u { width: 8.3333333333% }
    .-11u { margin-left: 91.6666666667% }
    .-10u { margin-left: 83.3333333333% }
    .-9u { margin-left: 75% }
    .-8u { margin-left: 66.6666666667% }
    .-7u { margin-left: 58.3333333333% }
    .-6u { margin-left: 50% }
    .-5u { margin-left: 41.6666666667% }
    .-4u { margin-left: 33.3333333333% }
    .-3u { margin-left: 25% }
    .-2u { margin-left: 16.6666666667% }
    .-1u { margin-left: 8.3333333333% }

When I remove the 4u class using chrome developer, the page is affected. However, when I delete this section from the css file, nothing happens. I am quite stumped in this, and it is really bugging me!

Answer 1

Read this spec: http://www.w3.org/International/questions/qa-escapes#cssescapes. The characters following the back slash represent a unicode code point. The space is required if the next character is allowed as part of the hexadecimal values.