Markdown links do not render `[example][1]\n[1]: http://example`

Standard links as supported by Github, Pandok, CommonMark and most other markdown tools don't seem to work in Readme.com, even if the documentation says ["The engine also supports all standard markdown constructs"][1]

[1]: https://docs.readme.com/rdmd/docs/syntax-extensions#standard-markdown

For example from the following 3 links, none will render:

Here are 3 styles of links that do not render: [example1][1], [example2][] and [example3][].
[1]\: http://example.com
[example2]\: http://example.com
[example3]\: http://example.com "link to example.com"

This style of links if far superior as it doesn't clutter the text with long links. What is the syntax to keep the link text and the URL separated in Readme.com markdown syntax?

CommonMark relevant spec paragraph: https://spec.commonmark.org/0.30/#link-reference-definition