code: function parse(node) {
    var link = {}
    var url = node.url || node.href || ''
    var start
    var end
    var page
  
    if (
      url.slice(0, GH_URL_PREFIX_LENGTH) !== GH_URL_PREFIX ||
      node.children.length !== 1 ||
      node.children[0].type !== 'text' ||
      toString(node).slice(0, GH_URL_PREFIX_LENGTH) !== GH_URL_PREFIX
    ) {
      return
    }
  
    start = GH_URL_PREFIX_LENGTH
    end = usernameEnd(url, GH_URL_PREFIX_LENGTH)
  
    if (end === -1 || url.charCodeAt(end) !== CC_SLASH) {
      return
    }
  
    link.user = url.slice(start, end)
  
    start = end + 1
    end = projectEnd(url, start)
  
    if (end === -1 || url.charCodeAt(end) !== CC_SLASH) {
      return
    }
  
    link.project = url.slice(start, end)
  
    start = end + 1
    end = url.indexOf('/', start)
  
    if (end === -1) {
      return
    }
  
    page = url.slice(start, end)
  
    if (page !== parse.COMMIT && page !== parse.ISSUE && page !== parse.PULL) {
      return
    }
  
    link.page = page
    start = end + 1
  
    if (page === parse.COMMIT) {
      end = shaEnd(url, start, true)
    } else {
      end = issueEnd(url, start)
    }
  
    if (end === -1) {
      return
    }
  
    link.reference = url.slice(start, end)
    link.comment = url.charCodeAt(end) === CC_HASH && url.length > end + 1
  
    return link
  }
docs: /* Parse a link and determine whether it links to GitHub.