+files. These empty files are contained within a directory named after
+the message-id.
+
+In what follows `encode()` represents a POSIX filesystem safe
+encoding. The encoding preserves alphanumerics, and the characters
+`+-_@=.,:`. All other octets are replaced with `%` followed by a two
+digit hex number.
+
+Currently :any:`notmuch-git` can read any format version, but can only
+create (via :any:`init`) :ref:`version 1 <format_version_1>` repositories.
+
+.. _format_version_0:
+
+Version 0
+---------
+
+This is the legacy format created by the `nmbug` tool prior to release
+0.37. For a message with Message-Id *id*, for each tag *tag*, there