createAnnotation = ($el, className) => {
        // Create a position an annotation relative to its offset parent.
        // We also store the element its annotation so we can reposition when
        // the window resizes.
        let $annotation = $("<div>")
            .addClass("tota11y")    // tota11y base class for styling
            .addClass(ANNOTATION_CLASS)
            .addClass(className)
            .css($el.position())
            .data({$el});

        // TODO: We can invoke a requestAnimationFrame(render) here to limit
        // the amount of times we run that timer

        // Append an object to the queue. We'll add the annotation to the DOM
        // later to reduce reflows.
        queue.push({
            $annotation: $annotation,
            $parent: $el.offsetParent()
        });

        return $annotation;
    }
Utility functions to annotate particular site elements.

Annotations are namespaced, meaning you would normally include this
package like so:

    let annotate = require("./annotate")("headers");

This allows plugins to easily maintain their annotations, rather than
keeping track of an extra class name elsewhere.