Use case:
You might want to link to specific areas of documentation. You would normally use an anchor, but anchors do not specifically call attention to the area you meant.

Create a pair of macros that allow you to anchor specific areas (a macro that creates a span with an ID should be sufficient) and a css directive that does something like:

<style>
#:target {
    background-color: #ffa;
    -webkit-transition: all 1s linear;
}</style>