Sample feed.xml Liquid template for use with Serif 0.3.2. Post unique IDs are independent of URL. Note the caveats!

feed.xml

layout: none

<?xml version="1.0" encoding="utf-8"?>

{% assign feed_url = "http://example.com/feed" %}
{% assign feed_title = "Example Feed" %}
{% assign feed_alternate = "http://example.com/blog" %}
{% assign feed_global_unique_id = "tag:example.com,2013:TOTALLY-RANDOM-STRING-OF-CHARACTERS-GOES-HERE" %}

{% assign feed_author_name = "J. Smith" %}
{% assign feed_author_url = "http://example.com/about" %}

{% assign feed_entry_tag_domain = "example.com" %}

<feed xmlns="http://www.w3.org/2005/Atom">
	<title>{{ feed_title }}</title>
	<link rel="self" type="application/atom+xml" href="{{ feed_url }}"/>
	<link rel="alternate" type="text/html" href="{{ feed_alternate }}"/>
	<id>{{ feed_global_unique_id }}</id>
	<updated>{{ site.latest_update_time | xmlschema }}</updated>
	<author>
		<name>{{ feed_author_name }}</name>
		<uri>{{ feed_author_url }}</uri>
	</author>
	{% for post in site.posts limit:10 %}
	<entry>
		<id>tag:{{ feed_entry_tag_domain }},{{ post.created | date: "%Y-%m-%d" }}:{{ post.created | date: "%s" }}</id>
		<title type="html">{{ post.title | smarty | replace:"&","&amp;" | replace:"<","&lt;" | replace:">","&gt;" }}</title>
		<updated>{{ post.updated | xmlschema }}</updated>
		<published>{{ post.created | xmlschema }}</published>
		<link href="{{ post.url }}" rel="alternate" type="text/html"/>
		<content type="html">{{ post.content | markdown | escape }}</content>
	</entry>
	{% endfor %}
</feed>

using-howto.md

To use

1. Change feed_url to where the feed will be served from.
2. Change feed_title to wahtever your feed's title should show up as in feed readers.
3. Set feed_alternate to the URL where the content can be seen as regular HTML.
4. feed_global_unique_id uses the tag: URI here, and should:
   1. have example.com changed to your blog domain,
   2. have 2013 changed to whatever year is appropriate for the feed starting,
   3. use a globally unique string of characters after the second :,
   4. most importantly, never ever change, even if the feed moves to a different domain or URL, or anything else --- change the ID and readers will assume entirely different content → posts will suddenly become duplicated in the likes of Google Reader.
5. Set your author name and a URL. In this template, it's used for all entries since each entry doesn't have its own author.
6. Change the feed_entry_tag_domain to be a domain name that should never change. This is used in tag: URIs for the entry ID. If this changes, the entry ID changes, and feed readers will see different content → posts will suddenly become duplicated in the likes of Google Reader. If you want to change ID scheme, make sure to keep the ID the same on older posts, using a conditional.