The box-shadow mixin

With all that you have learned about Less, you now can understand, build, and evaluate any complex Less code. To prove this, please open less/mixins.less and take a look at the box-shadow mixin (originally published on lesscss.org), which looks like the following code:

.box-shadow(@style, @c) when (iscolor(@c)) {
  -webkit-box-shadow: @style @c;
  -moz-box-shadow:    @style @c;
  box-shadow:         @style @c;
}
.box-shadow(@style, @alpha: 50%) when (isnumber(@alpha)) {
  .box-shadow(@style, rgba(0, 0, 0, @alpha));
}

To fully understand these mixins, you will have to know the basics of box-shadow in CSS3. The box-shadow properties accept a CSV list of shadows. A shadow consists of a list of two to four length values and a color. The first two length values describe the vertical and horizontal offsets related to the center of the box. These values are required but can be set to 0 to get an equal-size shadow around the box. The final values are optional and set the blur...