iex(1)> {:ok, lines} = Extractly.functiondoc("Extractly.moduledoc/2") |> hd()
      ...(1)> lines |> String.split("\n") |> Enum.take(3)
      ["  Returns docstring of a module", "", "  E.g. verbatim"]

      iex(2)> [{:ok, moduledoc}, {:error, message}] = Extractly.functiondoc(["Extractly.moduledoc/2", "Extactly.functiondoc/2"])
      ...(2)> moduledoc |> String.split("\n") |> Enum.take(4)
      [ "  Returns docstring of a module",
        "  E.g. verbatim",
        "",
        "      Extractly.moduledoc(\"Extractly\")"]
      ...(2)> message
      "Function doc for function Extactly.functiondoc/2 not found"

      iex(3)> [{:ok, out}, _] = Extractly.functiondoc(["moduledoc/2", "functiondoc/2"], module: "Extractly")
      ...(3)> String.split(out, "\n") |> hd()
      "  Returns docstring of a module"

      iex(4)> [{:ok, moduledoc}, {:ok, functiondoc}] = Extractly.functiondoc(["moduledoc/2", "functiondoc/2"], module: "Extractly", headline: 2)
      ...(4)> moduledoc |> String.split("\n") |> Enum.take(3)
      [ "## Extractly.moduledoc/2",
        "",
        "  Returns docstring of a module"]
      ...(4)> functiondoc |> String.split("\n") |> Enum.take(3)
      [ "## Extractly.functiondoc/2",
        "",
        "  Returns docstring of a function"]

      iex(5)> [{:ok, out}|_] = Extractly.functiondoc(:all, module: "Extractly", headline: 2)
      ...(5)> String.split(out, "\n") |> Enum.take(3)
      [ "## Extractly.do_not_edit_warning/1",
        "",
        "  Emits a comment including a message not to edit the created file, as it will be recreated from this template."]

      iex(6)> [ok: doc] = Extractly.functiondoc("Extractly.functiondoc/2", wrap_code_blocks: "elixir")
      ...(6)> doc |> String.split("\n") |> Enum.take(10)
      [ "  Returns docstring of a function",
        "  Ex:",
        "",
        "```elixir",
        "      iex(1)> {:ok, lines} = Extractly.functiondoc(\"Extractly.moduledoc/2\") |> hd()",
        "      ...(1)> lines |> String.split(\"\\n\") |> Enum.take(3)",
        "      [\"  Returns docstring of a module\", \"\", \"  E.g. verbatim\"]",
        "```",
        "",
        "  We can also pass a list of functions to get their docs concatenated"]

      iex(7)> {:ok, doc} = Extractly.moduledoc("Extractly")
      ...(7)> doc
      "  Provide easy access to information inside the templates rendered by `mix xtra`\n"

      iex(8)> {:ok, doc} = Extractly.moduledoc("Extractly", headline: 2)
      ...(8)> doc |> String.split("\n") |> Enum.take(3)
      [
        "## Extractly", "", "  Provide easy access to information inside the templates rendered by `mix xtra`"
      ]

      iex(9)> [{:ok, moduledoc} | _] =
      ...(9)>   moduledoc("Extractly", headline: 3, include: :all)
      ...(9)> moduledoc
      "### Extractly\n\n  Provide easy access to information inside the templates rendered by `mix xtra`\n"

      iex(10)> [_, {:ok, first_functiondoc} | _] =
      ...(10)>   moduledoc("Extractly", headline: 3, include: :all)
      ...(10)> first_functiondoc |> String.split("\n") |> Enum.take(5)
      [
        "### Extractly.do_not_edit_warning/1",
        "",
        "  Emits a comment including a message not to edit the created file, as it will be recreated from this template.",
        "",
        "  It is a convenience to include this into your templates as follows"
      ]

    iex(14)> Extractly.task("cmd", ~W[echo 42])
    "42\n"

    iex(15)> try do
    ...(15)>   Extractly.task("xxx")
    ...(15)> rescue
    ...(15)>   e in RuntimeError -> e.message |> String.split("\n") |> hd()
    ...(15)> end
    "The following output was produced wih error code 1"

    iex(11)> lines = [
    ...(11)>         "## Usage",
    ...(11)>         "### API",
    ...(11)>         "#### EarmarkParser.as_ast/2",
    ...(11)>         "### Support",
    ...(11)> ]
    ...(11)> toc(lines, gh_links: true)
    {:ok, [
      "- [Usage](#usage)",
      "  - [API](#api)",
      "    - [EarmarkParser.as_ast/2](#earmarkparseras_ast2)",
      "  - [Support](#support)",
    ]}

    iex(12)> lines = [
    ...(12)>         "## Usage",
    ...(12)>         "### API",
    ...(12)>         "#### EarmarkParser.as_ast/2",
    ...(12)>         "### Support",
    ...(12)> ]
    ...(12)> toc(lines)
    {:ok, [
      "- Usage",
      "  - API",
      "    - EarmarkParser.as_ast/2",
      "  - Support",
    ]}

    iex(13)> lines = [] # options are checked even if input is empty
    ...(13)> toc(lines, no_such_option: "x")
    {:error, "Unsupported option no_such_option"}

    iex(1)> render(["# Hello", "## World"])
    ["- Hello",  "  - World"]

    iex(2)> render(["# Hello", "## World"], type: :ol)
    ["1. Hello",  "   1. World"]

    iex(3)> render(["### Alpha", "ignored", "##### Alpha.1", "", "### Beta"])
    ["- Alpha", "  - Alpha.1", "- Beta"]

    iex(4)> render(["# First", "### Third (but will go to second level)", "## Second"], remove_gaps: true)
    ["- First", "  - Third (but will go to second level)", "  - Second"]

    iex(5)> lines = [
    ...(5)>         "## Usage",
    ...(5)>         "### API",
    ...(5)>         "#### EarmarkParser.as_ast/2",
    ...(5)>         "### Support",
    ...(5)> ]
    ...(5)> render(lines, gh_links: true)
    [
      "- [Usage](#usage)",
      "  - [API](#api)",
      "    - [EarmarkParser.as_ast/2](#earmarkparseras_ast2)",
      "  - [Support](#support)",
    ]

    iex(6)> render(["## One", "### Two"], format: :html)
    ["<ul>", "<li>One<ul>", "<li>Two</li>", "</ul></li>", "</ul>"]

    iex(7)> document = [
    ...(7)> "# Ignore",
    ...(7)> "# Too, but not what's below",
    ...(7)> "## Synopsis",
    ...(7)> "## Description",
    ...(7)> "### API",
    ...(7)> "#### too detailed",
    ...(7)> "### Tips & Tricks",
    ...(7)> "# Ignored again"
    ...(7)> ]
    ...(7)> render(document, format: :html, min_level: 2, max_level: 3, start: 5, type: :ol)
    [
      ~S{<ol start="5">},
      ~S{<li>Synopsis</li>},
      ~S{<li>Description<ol>},
      ~S{<li>API</li>},
      ~S{<li>Tips &amp; Tricks</li>},
      ~S{</ol></li>},
      ~S{</ol>},
    ]

    iex(8)> render(["# I", "## I.1", "## I.2", "### I.2.(i)", "# II", "### II.1.(ii)"], format: :push_list)
    ["I", :open, "I.1", "I.2", :open, "I.2.(i)", :close, :close, "II", :open, :open, "II.1.(ii)", :close, :close]

    iex(9)> render(["# I", "## I.1", "## I.2", "### I.2.(i)", "# II", "### II.1.(ii)"], format: :ast)
    ["I", ["I.1", "I.2", ["I.2.(i)"]], "II", [["II.1.(ii)"]]]

    iex(9)> render(["# Does not really matter"], format: :unknown)
    {:error, "Unsupported format: unknown in render"}