cmark

diff --git a/test/spec.txt b/test/spec.txt
@@ -13,12 +13,90 @@ license: '[CC-BY-SA 4.0](http://creativecommons.org/licenses/by-sa/4.0/)'
 Markdown is a plain text format for writing structured documents,
 based on conventions used for indicating formatting in email and
 usenet posts.  It was developed in 2004 by John Gruber, who wrote
-the first Markdown-to-HTML converter in perl, and it soon became
-widely used in websites.  By 2014 there were dozens of
-implementations in many languages.  Some of them extended basic
-Markdown syntax with conventions for footnotes, definition lists,
-tables, and other constructs, and some allowed output not just in
-HTML but in LaTeX and many other formats.
+the first Markdown-to-HTML converter in Perl, and it soon became
+ubiquitous.  In the next decade, dozens of implementations were
+developed in many languages.  Some extended the original
+Markdown syntax with conventions for footnotes, tables, and
+other document elements.  Some allowed Markdown documents to be
+rendered in formats other than HTML.  Websites like Reddit,
+StackOverflow, and GitHub had millions of people using Markdown.
+And Markdown started to be used beyond the web, to author books,
+articles, slide shows, letters, and lecture notes.
+
+What distinguishes Markdown from many other lightweight markup
+syntaxes, which are often easier to write, is its readability.
+As Gruber writes:
+
+> The overriding design goal for Markdown's formatting syntax is
+> to make it as readable as possible. The idea is that a
+> Markdown-formatted document should be publishable as-is, as
+> plain text, without looking like it's been marked up with tags
+> or formatting instructions.
+> (<http://daringfireball.net/projects/markdown/>)
+
+The point can be illustrated by comparing a sample of
+[AsciiDoc](http://www.methods.co.nz/asciidoc/) with
+an equivalent sample of Markdown.  Here is a sample of
+AsciiDoc from the AsciiDoc manual:
+
+```
+1. List item one.
++
+List item one continued with a second paragraph followed by an
+Indented block.
++
+.................
+$ ls *.sh
+$ mv *.sh ~/tmp
+.................
++
+List item continued with a third paragraph.
+
+2. List item two continued with an open block.
++
+--
+This paragraph is part of the preceding list item.
+
+a. This list is nested and does not require explicit item
+continuation.
++
+This paragraph is part of the preceding list item.
+
+b. List item b.
+
+This paragraph belongs to item two of the outer list.
+--
+```
+
+And here is the equivalent in Markdown:
+```
+1.  List item one.
+
+    List item one continued with a second paragraph followed by an
+    Indented block.
+
+        $ ls *.sh
+        $ mv *.sh ~/tmp
+
+    List item continued with a third paragraph.
+
+2.  List item two continued with an open block.
+
+    This paragraph is part of the preceding list item.
+
+    1. This list is nested and does not require explicit item continuation.
+
+       This paragraph is part of the preceding list item.
+
+    2. List item b.
+
+    This paragraph belongs to item two of the outer list.
+```
+
+The AsciiDoc version is, arguably, easier to write. You don't need
+to worry about indentation.  But the Markdown version is much easier
+to read.  The nesting of list items is apparent to the eye in the
+source, not just in the processed document.
 
 ## Why is a spec needed?