Append content under the current cursor position or given lnum of the buffer

import { Denops } from "../mod.ts";
import * as fn from "../function/mod.ts";
import { append, open } from "../buffer/mod.ts";

export async function main(denops: Denops): Promise<void> {
  await open(denops, "README.md");
  const bufnr = (await fn.bufnr(denops)) as number;
  // Append the content under the cursor position of the `bufnr` buffer
  await append(denops, bufnr, ["Hello", "World"]);
}

It temporary change modified, modifiable, and foldmethod options to append the content of the buffer buffer without unmodifiable error or so on.