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

[1]: http://example.com

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

[website]: http://example.com

Here's [one][case] with an upper case label definition.

[CASE]: http://example.com

Here's [one]
[website] with definition name on the next line.

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

Here's a [multiline
one][website] defined on 2 lines.