metadata blocks - pulldown-cmark guide

Run this with cargo test --features gen-tests suite::metadata_blocks.

Examples and edge cases for metadata blocks.

YAML-style and pluses-style metadata blocks are supported.

YAML-style metadata blocks:

Pluses-style metadata blocks:

In both cases, only trailing spaces can be in the delimiting lines.

All metadata blocks must be ended, EOF is not a valid ending of the block.

Basic usage:

---
title: example
another_field: 0
---

EOF is not a valid ending of the block:

---
title: example
another_field: 0

<hr>
<p>title: example
another_field: 0</p>

A metadata block cannot be empty:

---
---

<hr>
<hr>

A blank line cannot be after the start of the metadata block:

---

title: example
another_field: 0
---

<hr>
<h2>title: example
another_field: 0</h2>

A metadata block cannot interrumpt a paragraph:

My paragraph here.
---
title: example
another_field: 0
---

<h2>My paragraph here.</h2>
<h2>title: example
another_field: 0</h2>

But it can be after a blank line:

My paragraph here.

---
title: example
another_field: 0
---

<p>My paragraph here.</p>

After the start sequence nothing but spaces can be in the same line:

---    
title: example
another_field: 0
---

--- -
title: example
another_field: 0
---

<hr>
<h2>title: example
another_field: 0</h2>

The same applies for the end sequence:

---
title: example
another_field: 0
---        

---
title: example
another_field: 0
---a

<hr>
<p>title: example
another_field: 0
---a</p>

The end sequence for YAML-style blocks can be three dots:

---
title: example
another_field: 0
...

Finally, pluses-style blocks also work following the same rules except the closing sequence must be +++:

+++
title: example
another_field: 0
+++

Metadata blocks cannot be indented:

    ---
    Things
    ---

<pre><code>---
Things
---
</code></pre>

Metadata blocks may contain lists:

---
- Item 1
- Item 2
---