lib: document config metadata

This probably should have been part of 3458e3c89c, but I missed it.

diff --git a/lib/database.cc b/lib/database.cc
index 86bf26192079bcbcf9f5475556d0ad71be2fef0b..2b2d8219d29e5e963517b2a9c5219dec56be83dc 100644 (file)
--- a/lib/database.cc
+++ b/lib/database.cc
@@ -185,6 +185,14 @@ typedef struct {
  *                     generated is 1 and the value will be
  *                     incremented for each thread ID.
  *
+ *     C*              metadata keys starting with C indicate
+ *                     configuration data. It can be managed with the
+ *                     n_database_*config* API.  There is a convention
+ *                     of hierarchical keys separated by '.' (e.g.
+ *                     query.notmuch stores the value for the named
+ *                     query 'notmuch'), but it is not enforced by the
+ *                     API.
+ *
  * Obsolete metadata
  * -----------------
  *