atom.xml is not valid

[Leon0824]

Bug Report

Environment

Zola version: 0.12.2

Expected Behavior

Valid atom.xml from W3C Validation Service

Current Behavior

Not valid.

1. Missing <author>, <author> should be added by whole feed or by every entry.
2. <content> part should be

<content type="xhtml">
  <div xmlns="http://www.w3.org/1999/xhtml">
    {{ page.content }}
  </div>
</content>     

Step to reproduce

Submit a Zola atom feed to the W3C Validation Service

[Keats]

Hmm I didn't know author was mandatory...

[kuon]

This is my template that validate:

<?xml version="1.0" encoding="UTF-8"?>
<feed xmlns="http://www.w3.org/2005/Atom" xml:lang="{{ lang }}">
  <title>{{ config.title }}
  {%- if term %} - {{ term.name }}
  {%- elif section.title %} - {{ section.title }}
  {%- endif -%}
</title>
{%- if config.description %}
<subtitle>{{ config.description }}</subtitle>
{%- endif %}
<link href="{{ feed_url | safe }}" rel="self" type="application/atom+xml"/>
<link href="
  {%- if section -%}
  {{ section.permalink | escape_xml | safe }}
  {%- else -%}
  {{ config.base_url | escape_xml | safe }}
  {%- endif -%}
  "/>
<generator uri="https://www.getzola.org/">Zola</generator>
<updated>{{ last_updated | date(format="%+") }}</updated>
<id>{{ feed_url | safe }}</id>
{%- for page in pages %}
{%- if not page.extra.ignore_feed %}
<entry xml:lang="{{ page.lang }}">
  <title>{{ page.title }}</title>
  <published>{{ page.date | date(format="%+") }}</published>
  <updated>{{ page.updated | default(value=page.date) | date(format="%+") }}</updated>
  <link href="{{ page.permalink | safe }}" type="text/html"/>
  <id>{{ page.permalink | safe }}</id>
  <author>
    <name>{{ page.extra.author | default(value=config.extra.author) }}</name>
  </author>
  <content type="html">
      {{ page.content  }}
  </content>
</entry>
{%- endif %}
{%- endfor %}
</feed>

[Keats]

Yeah the only issue is that author would be optional so it's possible that no one fills it. Would an empty value for the author still validate? It's also annoying since if we want to ensure validation, we'd likely need to promote author out of extra which sucks :/

[Keats]

Closing as duplicate of #2024 which is less likely to be forgotten as it's more recent and has some ideas.