Added why-cmark-and-not-x page.

Author: jgm

why-cmark-and-not-x.md

@@ -0,0 +1,86 @@
+Why use `cmark` and not X?
+==========================
+
+`hoedown`
+---------
+
+`hoedown` (which derives from `sundown`) is slightly faster
+than `cmark` in our benchmarks (0.21s vs. 0.29s).  But both
+are much faster than any other available implementations.
+
+`hoedown` boasts of including "protection against all possible
+DOS attacks," but there are some chinks in the armor:
+
+    % time python -c 'print(("[" * 50000) + "a" + ("]" * 50000))' | cmark
+    ...
+    user 0m0.073s
+    % time python -c 'print(("[" * 50000) + "a" + ("]" * 50000))' | hoedown
+    ...
+    0m17.84s
+
+`hoedown` has many parsing bugs.  Here is a selection:
+
+    % hoedown
+    - one
+      - two
+        1. three
+    ^D
+    <ul>
+    <li>one
+
+    <ul>
+    <li>two</li>
+    <li>three</li>
+    </ul></li>
+    </ul>
+
+
+    % hoedown
+    ## hi\###
+    ^D
+    <h2>hi\</h2>
+
+
+    % hoedown
+    [ΑΓΩ]: /φου
+
+    [αγω]
+    ^D
+    <p>[αγω]</p>
+
+
+    % hoedown
+    ```
+    [foo]: /url
+    ```
+
+    [foo]
+    ^D
+    <p>```</p>
+
+    <p>```</p>
+
+    <p><a href="/url">foo</a></p>
+
+
+    % hoedown
+    [foo](url "ti\*tle")
+    ^D
+    <p><a href="url" title="ti\*tle">foo</a></p>
+
+
+`discount`
+----------
+
+`cmark` is about six times faster.
+
+`kramdown`
+----------
+
+`cmark` is about a hundred times faster.
+
+`kramdown` also gets tied in knots by pathological input like
+
+    python -c 'print(("[" * 50000) + "a" + ("]" * 50000))'
+
+