parseKeys = function parseQueryStringKeys(givenKey, val, options, valuesParsed) {
    if (!givenKey) {
        return;
    }

    // Transform dot notation to bracket notation
    var key = options.allowDots ? givenKey.replace(/\.([^.[]+)/g, '[$1]') : givenKey;

    // The regex chunks

    var brackets = /(\[[^[\]]*])/;
    var child = /(\[[^[\]]*])/g;

    // Get the parent

    var segment = options.depth > 0 && brackets.exec(key);
    var parent = segment ? key.slice(0, segment.index) : key;

    // Stash the parent if it exists

    var keys = [];
    if (parent) {
        // If we aren't using plain objects, optionally prefix keys that would overwrite object prototype properties
        if (!options.plainObjects && has$1.call(Object.prototype, parent)) {
            if (!options.allowPrototypes) {
                return;
            }
        }

        keys.push(parent);
    }

    // Loop through children appending to the array until we hit depth

    var i = 0;
    while (options.depth > 0 && (segment = child.exec(key)) !== null && i < options.depth) {
        i += 1;
        if (!options.plainObjects && has$1.call(Object.prototype, segment[1].slice(1, -1))) {
            if (!options.allowPrototypes) {
                return;
            }
        }
        keys.push(segment[1]);
    }

    // If there's a remainder, just add whatever is left

    if (segment) {
        keys.push('[' + key.slice(segment.index) + ']');
    }

    return parseObject(keys, val, options, valuesParsed);
}
Parse a HTTP token list.

@param {string} str
@private