Here's a [reference link][1].

[1]: http://parsedown.org

Here's [one] [2] with an alternative syntax.

[2] :http://parsedown.org

Here's [one][3] on the next line.
[3]: http://parsedown.org

Here's [one][4] on 2 lines.

[4]:
http://parsedown.org

Here's [one][5] with a different URL.

[5]: http://parsedown.org/tests/

Here's [one][the website] with a semantic name.

[the website]: http://parsedown.org

Here's [one][404] with no definition.

Here's an image: ![Markdown Logo][image]

[image]: https://raw.github.com/dcurtis/markdown-mark/master/png/32x20-solid.png