{{ $author := index .Site.Data.authors ((or .Params.author .Site.Author.default.user) | default "default") }}

<tab-list>
  <a href="{{ .Site.BaseURL }}/{{ $author.user }}">Messages</a>
  <a href="{{ .Site.BaseURL }}/{{ $author.user }}/feeds/">Feeds</a>
  <a href="{{ .Site.BaseURL }}/{{ $author.user }}/media/">Media</a>
  <a href="{{ .Site.BaseURL }}/{{ $author.user }}/likes/">Likes</a>
</tab-list>