HTML5 ol polyfill

if (!('reversed' in document.createElement('ol'))) {
    (function () {
        'use strict';
        // Run the code on each ordered list with a "reversed" attribute.
        var lists = document.getElementsByTagName('ol'),    // All ol elements
            length = lists.length,  // Number of ol elements
            i,                      // Counter var
            j,                      // Counter var
            child,                  // ol element
            currChildren,           // li elements for a given ol element
            childrenLength,         // Number of li elements
            start,                  // Value of ol start attribute
            currCount,              // Value to be used in li value attribute
            val;                    // Value from li value attribute
        for (i = 0; i < length; i++) {
            child = lists[i];
            if (child.getAttribute('reversed') !== null) {
                currChildren = child.getElementsByTagName('li');
                childrenLength = currChildren.length;
                start = child.getAttribute('start');
                // Check the existence of the start attribute and if it's
                // a number.
                if (start !== null && !isNaN(start)) {
                    currCount = start;
                } else {
                    // Do this if the start attribute is not present. The first
                    // number is derived from the number of list items.
                    // (Ugh; Do we need double loops to get the correct count?)
                    currCount = 0;
                    for (j = 0; j < childrenLength; j++) {
                        if (currChildren[j].parentNode === child) {
                            currCount++;
                        }
                    }
                }
                // Go through each list item, adding the 'value' attribute
                // plus currCount number then subtract one from currCount
                // so we're ready for the next one.
                for (j = 0; j < childrenLength; j++) {
                    if (currChildren[j].parentNode === child) {
                        // Per spec, if set, the value attribute should be used
                        // and renumbering started from there.
                        val = currChildren[j].getAttribute('value');
                        if (val !== null && !isNaN(val)) {
                            currCount = val;
                        }
                        currChildren[j].setAttribute('value', currCount);
                        currCount -= 1;
                    }
                }
            }
        }
    }());
}