# Preserve blank lines

By default MD4C (like CommonMark) treats any run of blank lines between two
blocks as a single block boundary and discards how many blank lines it
consisted of.

With the flag `MD_FLAG_PRESERVEBLANKLINES`, each such run is instead reported
as a single block `MD_BLOCK_BLANK` whose detail (`MD_BLOCK_BLANK_DETAIL`) holds
the count of blank lines forming the separation. This lets applications
reproduce the vertical spacing of the source; it is a deviation from
CommonMark.

The `md2html` renderer used for these tests renders a run of `line_count` blank
lines as `line_count - 1` `<br>` elements: one blank line is the ordinary block
separation CommonMark already implies (and is already visible as the boundary
between the two blocks), so only the surplus blank lines are shown.

A run of several blank lines between two blocks renders as `line_count - 1`
`<br>` elements:

```````````````````````````````` example
Paragraph one.



Paragraph two.
.
<p>Paragraph one.</p>
<br>
<br>
<p>Paragraph two.</p>
.
--fpreserve-blank-lines
````````````````````````````````

An ordinary single blank line separating two blocks is still reported by the
parser (as a `MD_BLOCK_BLANK` with `line_count` 1), but this renderer shows
nothing extra for it, as that first blank line is the block separation already
implied by the boundary between the two paragraphs:

```````````````````````````````` example
foo

bar
.
<p>foo</p>
<p>bar</p>
.
--fpreserve-blank-lines
````````````````````````````````

Blank lines leading the document are reported:

```````````````````````````````` example


foo
.
<br>
<p>foo</p>
.
--fpreserve-blank-lines
````````````````````````````````

Blank lines trailing the document are reported:

```````````````````````````````` example
foo


.
<p>foo</p>
<br>
.
--fpreserve-blank-lines
````````````````````````````````

Blank lines preceding a container are reported before it:

```````````````````````````````` example
foo


> quote
.
<p>foo</p>
<br>
<blockquote>
<p>quote</p>
</blockquote>
.
--fpreserve-blank-lines
````````````````````````````````

Blank lines inside a block quote are reported inside it:

```````````````````````````````` example
> foo
>
>
> bar
.
<blockquote>
<p>foo</p>
<br>
<p>bar</p>
</blockquote>
.
--fpreserve-blank-lines
````````````````````````````````

Blank lines inside a block quote followed by blank lines after it are split on
the boundary: the ones inside the quote are reported inside it, and the ones
after it are reported at the outer level.

```````````````````````````````` example
> foo
>
>

bar
.
<blockquote>
<p>foo</p>
<br>
</blockquote>
<p>bar</p>
.
--fpreserve-blank-lines
````````````````````````````````

Blank lines separating two block quotes are reported between them:

```````````````````````````````` example
> foo


> bar
.
<blockquote>
<p>foo</p>
</blockquote>
<br>
<blockquote>
<p>bar</p>
</blockquote>
.
--fpreserve-blank-lines
````````````````````````````````

Blank lines inside a fenced code block are part of its verbatim contents and
are not reported as `MD_BLOCK_BLANK`:

```````````````````````````````` example
```
foo



bar
```
.
<pre><code>foo



bar
</code></pre>
.
--fpreserve-blank-lines
````````````````````````````````

Likewise, blank lines inside an indented code block are not reported:

```````````````````````````````` example
    foo


    bar
.
<pre><code>foo


bar
</code></pre>
.
--fpreserve-blank-lines
````````````````````````````````