-You can add other tags to `THREAD_TAGS` as needed. Note that this is one way
-only; you need to explicitly remove the tag from all the messages in a thread to
-stop it from propagating again.
+You can add other tags to `THREAD_TAGS` as needed. Note that this is
+one way only; you need to explicitly remove the tag from all the
+messages in a thread to stop it from propagating again. See
+[notmuch-search-terms](https://notmuchmail.org/doc/latest/man7/notmuch-search-terms.html)
+for discussion of `thread:{}` queries.
+
+
+## How can I extract a git patchset for an email thread?
+
+See
+[notmuch-extract-patch](https://github.com/aaptel/notmuch-extract-patch). See
+also notmuch-extract-patch in
+[mailscripts](https://git.spwhitton.name/mailscripts/).
+
+## T150-tagging.sh is failing with Xapian 1.4.6
+
+This is (probably) a bug in this point release of Xapian, should be
+fixed in 1.4.7. Try reverting Xapian commit
+`093999529acc2f86900d91fed0c7f7af301ab94a`, e.g. with the following
+patch.
+
+
+ index 80e578b85..a47f14a68 100644
+ --- a/xapian-core/backends/glass/glass_postlist.cc
+ +++ b/xapian-core/backends/glass/glass_postlist.cc
+ @@ -759,7 +759,7 @@ GlassPostList::open_nearby_postlist(const std::string & term_,
+ (void)need_pos;
+ if (term_.empty())
+ RETURN(NULL);
+ - if (!this_db.get() || this_db->postlist_table.is_modified())
+ + if (!this_db.get() || this_db->postlist_table.is_writable())
+ RETURN(NULL);
+ RETURN(new GlassPostList(this_db, term_, cursor->clone()));
+ }
+