docs: function mergeChildren$(children) {
    if (!Array.isArray(children)) {
      children = [children];
    }
    children = flatten(children).filter(_ => _ !== null);
    let childrenVdom$arr = children.map(child => {
      if (isStream(child)) {
        return child.flatMap(mergeChildren$);
      }
      return child;
    });
  
    return merge$(childrenVdom$arr);
  }