code: function definition(node) {
    var content = uri(node.url)
  
    if (node.title) {
      content += space + title(node.title)
    }
  
    return (
      leftSquareBracket +
      (node.label || node.identifier) +
      rightSquareBracket +
      colon +
      space +
      content
    )
  }
docs: Stringify an URL definition.  Is smart about enclosing `url` (see `encloseURI()`) and `title` (see `encloseTitle()`).  ```markdown [foo]: <foo at bar dot com> 'An "example" e-mail' ```