+(defun notmuch-hex-encode (str)
+ "Hex-encode STR (e.g., as used by batch tagging).
+
+This replaces spaces, percents, and double quotes in STR with
+%NN where NN is the hexadecimal value of the character."
+ (replace-regexp-in-string
+ "[ %\"]" (lambda (match) (format "%%%02x" (aref match 0))) str))
+