Working with Bootstrap's default system of 4 screen size ranges, I wanted a way to know, quickly and visually, which size BS is reporting on each page view.

Here's a quick snippet which will create 4 divs, each visible only to the Bootstrap screen size currently in use.

view plain print about
2        <cfloop list="xs,sm,md,lg" index="i">
3            <span class="visible-#i#">#i#</span>
4        </cfloop>
5    </div>

As you resize your browser window, the value changes. Simple.