Created a.datechar and a.certainty

Replaced multiple attribute definitions with refs

ead_revised.rng

@@ -494,9 +494,7 @@ For these and/or other purposes and motivations, and without any expectation of
 			<ref name="am.dates.era"/>
 			<ref name="am.dates.calendar"/>
 			<ref name="am.date.normal"/>
-			<optional>
-				<attribute name="certainty"/>
-			</optional>
+			<ref name="a.certainty"/>
 			<ref name="a.encodinganalog"/>
 			<ref name="m.mixed.basic"/>
 		</element>
@@ -690,15 +688,11 @@ For these and/or other purposes and motivations, and without any expectation of
 			<ref name="a.common"/>
 			<ref name="a.label"/>
 			<ref name="a.unitdatetype"/>
-			<optional>
-				<attribute name="datechar"/>
-			</optional>
+			<ref name="a.datechar"/>
+			<ref name="a.certainty"/>
 			<ref name="am.dates.era"/>
 			<ref name="am.dates.calendar"/>
 			<ref name="am.date.normal"/>
-			<optional>
-				<attribute name="certainty"/>
-			</optional>
 			<ref name="a.encodinganalog"/>
 			<ref name="m.mixed.basic"/>
 		</element>
@@ -709,13 +703,9 @@ For these and/or other purposes and motivations, and without any expectation of
 			<ref name="a.common"/>
 			<ref name="a.label"/>
 			<ref name="a.unitdatetype"/>
-			<optional>
-				<attribute name="certainty"/>
-			</optional>
+			<ref name="a.datechar"/>
+			<ref name="a.certainty"/>
 			<ref name="a.encodinganalog"/>
-			<optional>
-				<attribute name="datechar"/>
-			</optional>
 			<ref name="am.dates.era"/>
 			<ref name="am.dates.calendar"/>
 			<choice>
@@ -2901,6 +2891,18 @@ For these and/or other purposes and motivations, and without any expectation of
 			</attribute>
 		</optional>
 	</define>
+
+	<define name="a.datechar">
+		<optional>
+			<attribute name="datechar"/>
+		</optional>
+	</define>
+
+	<define name="a.certainty">
+		<optional>
+			<attribute name="certainty"/>
+		</optional>
+	</define>
 
 	<!-- ATTRIBUTE VALUE LISTS -->