Find regexp of valid attribute names

gistfile1.js

var valid_first = [];
var valid_second = [];
for (var i = 0, len = 0xFFFF; i < len; i++) {
    try{
        var char = String.fromCharCode(i);
        if(char.toLowerCase() != char.toUpperCase() && valid_second.indexOf(char.toLowerCase().charCodeAt(0)) >= 0){
            continue;
        }
        document.body.setAttribute('a' + char, '');
        document.body.removeAttribute('a' + char);
        valid_second.push(i);
        document.body.setAttribute(char, '');
        document.body.removeAttribute(char, '');
        valid_first.push(i);
    }catch(e){}
}

function charRepr(char){
    var str = String.fromCharCode(char);
    if(char < 0xFF || str.toLowerCase() !== str.toUpperCase()){
        if(str == '.' || str == '-' || str == ']') {
            return '\\' + str;
        }
        return str;
    } else {
        return '\\u' + ('00' + Number(char).toString(16).toUpperCase()).substr(-4);
    }
}

function makeRanges(list) {
    var ranges = [];
    var rangeStart = list[0];
    var currentRangeLength = 1;
    for (var i = 1, len = list.length; i < len; i++) {
        if(list[i] !== rangeStart + currentRangeLength) {
            if(currentRangeLength === 1){
                ranges.push(charRepr(rangeStart));
            } else {
                ranges.push(charRepr(rangeStart) + '-' + charRepr(list[i-1]));
            }
            currentRangeLength = 1;
            rangeStart = list[i];
        } else {
            currentRangeLength++;
        }
    }
    return ranges.join('');
}
var ranges_start = makeRanges(valid_first);
var ranges_cont = makeRanges(valid_second);
var regexp_source = '[' + ranges_start + '][' + ranges_cont + ']*';
console.log(regexp_source);