Markdown: Link reference definitions

language: "markdown"

This doesn't precisely follow the link reference definition specification, but should be a "good enough" implementation

A link reference definition, like all markdown paragraphs, can be indented up to 3 spaces. It has the pattern [<label>]: where <label> is characters containing at least 1 non-whitespace character.

If a single long line is wrapped, created lines are indented 4 spaces, to match footnotes.

[link]: /url "link title"          ->     [link]: /url    ¦
                ¦                             "link title"¦

Link reference definitions do not interrupt a paragraph; ie. there must be a blank line between one and a normal paragraph. If there's no blank line it'll be treated as part of the paragraph.

paragraph        ¦                        paragraph text   ¦
text [link]      ¦                 ->     [link] [link]:   ¦
[link]: some_url ¦                        some_url         ¦

LDRs consist of just a single paragraph, and no blank line is required between multiple LRDs.

text [one]         ¦                      text [one] text    ¦
text [two]         ¦                      [two]              ¦
                   ¦               ->                        ¦
[one]: url1 description                   [one]: url1        ¦
  [two]: url2      ¦                          description    ¦
                                            [two]: url2      ¦

LRDs are terminated by any of the normal paragraph-interrupting blocks, like fenced code block or list item.

[one]:    ¦                               [one]: url¦
 url      ¦                               - list    ¦
- list item                                 item    ¦
          ¦                                         ¦
[two]:    ¦                        ->     [two]: url¦
    url   ¦                               ``` js    ¦
``` js    ¦                               let i;    ¦
let i;    ¦                               ```       ¦
```       ¦                                         ¦