parse_tag_command_line (void *ctx, int argc, char **argv,
char **query_str, tag_op_list_t *ops);
+/*
+ * Test tags for some forbidden cases.
+ *
+ * Relax the checks if 'remove' is true to allow removal of previously
+ * added forbidden tags.
+ *
+ * return: NULL if OK,
+ * explanatory message otherwise.
+ */
+const char *
+illegal_tag (const char *tag, notmuch_bool_t remove);
+
/*
* Create an empty list of tag operations
*