sort of looks like a regexp parser; will use regexp instead

wrap.js

var wrap = (list, test, cb) => {
	const stack = [];
	let start, end, lastTest, result, lastItem, item, out;
	for (let i=0,len=list.length; i<len; i++) {
		item = list.splice(i,1)[0];
		result = test(item, lastItem);
		if ((!result && lastTest !== result) || (i === list.length-1 && lastTest === result)) {
			out = cb(item, i, start, end, stack, lastItem);
			if (null != out) {
				list.splice(i, 0, ...out);
				i += out.length;
			}
			end = start = undefined;
			stack.splice(0);
		}
		else {
			if (null == start) start = i;
			end = i;
			if (0 === stack.length || stack[0].lvl < item.lvl) stack.unshift(item);
			else while (stack.length > 0 && stack[0].lvl > item.lvl) stack.pop();
		}
		lastTest = result;
		lastItem = item;
	}
};