-void *open_settings_w(char *sessionname);
-void write_setting_s(void *handle, char *key, char *value);
-void write_setting_i(void *handle, char *key, int value);
+void *open_settings_w(const char *sessionname, char **errmsg);
+void write_setting_s(void *handle, const char *key, const char *value);
+void write_setting_i(void *handle, const char *key, int value);
+void write_setting_filename(void *handle, const char *key, Filename value);
+void write_setting_fontspec(void *handle, const char *key, FontSpec font);