What is the value of the css 'ex' unit?

Question

(Not to be confused with Xunit, a popular .Net unit testing library.)

Today in a fit of boredom I started inspecting Gmails DOM (yes, I was very bored).

Ever

Answer 1

To answer the question, one use is with superscript and subscript. Example:

sup {
    font-size: 75%;
    height: 0;
    line-height: 0;
    position: relative;
    vertical-align: baseline;
    bottom: 1ex;
}