function load(filename, root, callback) {
        if (typeof root === "function") {
            callback = root;
            root = new protobuf.Root();
        } else if (!root)
            root = new protobuf.Root();
        return root.load(filename, callback);
    }
Build type, one of `"full"`, `"light"` or `"minimal"`.
@name build
@type {string}
@const