Missing documentation on how to write site configuration files

I recently opened a PR to add a site configuration file: https://github.com/fivefilters/ftr-site-config/pull/1994.

This PR was improved by a maintainer to get better support in wallabag:

@@ -1,3 +1,8 @@
 title: //main//header//h1
+date: //header//time/@datetime
 body: //main//article//div[@id="post-content"]
+
+prune: no
+tidy: no
+
 test_url: https://www.d12frosted.io/posts/2025-12-06-vui-under-the-hood

The site configuration was later improved by the same maintainer again in a different PR:

@@ -2,7 +2,11 @@ title: //main//header//h1
 date: //header//time/@datetime
 body: //main//article//div[@id="post-content"]
 
+# [wallabag] activate images
+strip_attr: //img[contains(@src, '/')]/@srcset
+
 prune: no
 tidy: no
 
 test_url: https://www.d12frosted.io/posts/2025-12-06-vui-under-the-hood
+test_url: https://www.d12frosted.io/posts/2026-06-30-vulpea-schemas

We could maybe improve the documentation so contributors get it right themselves. For example, wallabag documentation could mention:

• that several test_url can be provided
• that date is being used by Wallabag if provided
• that prune and tidy can be used to improve rendering (but it's not clear for me what should be done: are we expecting the contributor to try all combinations of these 2 flags and compare the end results?)
• what strip_attr is about (I can't find any reference in any documentation) and when to use it