empty preferred content

* Document that settting preferred content to "" is the same as the
  default unset behavior.
* sync: Avoid misleading warning about future preferred content
  transition when preferred content is set to "".

doc/forum/Unable_to_delete_preferred-content.log/comment_3_ef3f7b7c14f44b79785ca9ab5b23ca0f._comment

@@ -0,0 +1,24 @@
+[[!comment format=mdwn
+ username="joey"
+ subject="""comment 3"""
+ date="2024-12-13T16:52:18Z"
+ content="""
+Ah, you're right that this future change in `git-annex sync` behavior is
+one way that "anything" is different from not configured.
+
+It turns out that you can just use `git-annex wanted here ""` to get back
+the same behavior as the preferred content being unset. I had forgotten
+about that, and it was not really documented anywhere, which I've
+corrected.
+
+Running `git-annex sync` without --content with preferred content set to ""
+currently warns about the transition, but that warning is false. I'm fixing
+it to not warn in this case.
+
+As to the heroic measures, .git/annex/index gets merged into whatever is in
+the git-annex branch, so you need to delete that file as well as rewriting
+the branch. And you need to do this in every single repository that has
+received the unwanted change. And since it also auto-merges git-annex
+branches from remotes, you probably will want to temporarily remove the
+remote tracking branches from git's ref list.
+"""]]

doc/git-annex-preferred-content.mdwn

@@ -30,6 +30,9 @@ a file matches, the repository wants to store its content. If it doesn't,
 the repository wants to drop its content (if there are enough copies
 elsewhere to allow removing it).
 
+An empty preferred content expression is treated the same as preferred
+content not being configured.
+
 # EXPRESSIONS
 
 * `include=glob` / `exclude=glob`