/usr/share/gconf/schemas/notification.schemas is in xchat-gnome-common 1:0.30.0~git20131003.d20b8d+really20110821-0.2ubuntu12.2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 | <gconfschemafile>
	<schemalist>
		<schema>
			<key>/schemas/apps/xchat/plugins/notification/level</key>
			<applyto>/apps/xchat/plugins/notification/level</applyto>
			<owner>xchat</owner>
			<type>int</type>
			<default>3</default>
			<gettext_domain>xchat-gnome</gettext_domain>
			<locale name="C">
				<short>Level of the messages that require a notification</short>
				<long>Messages are classified according to their importance. 
				Select level of messages above which the notification icon will be displayed.
				Valid values are: "0" (always displayed), "1" (all messages including information),
				"2" (all channel messages), "3" (only private or highlighted messages).
				</long>
			</locale>
		</schema>
	</schemalist>
</gconfschemafile>
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