Here's a reference link.
Here's one on the next line.
Here's one with a different URL.
Here's one with a semantic name.
Here's one with an upper case label definition.
Here's one with definition name on the next line.
Here's [one][404] with no definition.
Here's an image:
Here's an implicit one.
Here's an implicit one with an empty link definition.
Here's a multiline one defined on 2 lines.