--- modules/damieng/clean_xml/loncapa.xsd	2015/12/23 19:38:13	1.18
+++ modules/damieng/clean_xml/loncapa.xsd	2017/01/05 16:55:16	1.19
@@ -147,6 +147,7 @@
     </xs:annotation>
     <xs:complexType mixed="true">
       <xs:choice maxOccurs="unbounded" minOccurs="0">
+        <xs:element ref="head"/>
         <xs:group ref="text-with-parts"/>
         <xs:group ref="inserts"/>
         <xs:element ref="allow"/>
@@ -2250,6 +2251,7 @@
     <xs:annotation>
       <xs:documentation>
         Query for a chemical reaction.
+        An internal textline element is necessary for the student's response to go in.
       </xs:documentation>
     </xs:annotation>
     <xs:complexType mixed="true">
@@ -2262,11 +2264,24 @@
         <xs:group ref="text-only"/>
       </xs:choice>
       <xs:attributeGroup ref="response-identification"/>
-      <xs:attribute name="answer" type="xs:string" use="required"/>
+      <xs:attribute name="answer" type="xs:string" use="required">
+        <xs:annotation>
+          <xs:documentation>
+            The correct answer.
+            Chemical reactions use the following syntax:
+            - Reactants are separated from products by '-&gt;'.
+            - Individual reactants and products are separated by ' +' (leading space is obligatory).
+            - Numbers preceding the first symbol of a chemical specie are considered to be stoichiometric coefficients.
+            - Numbers appearing after the first symbol of a chemical specie are considered to be subscripts.
+            - Superscripts are initialized by '^' and terminated by a space.
+            - Ionic charges are superscripts composed of a number followed by a sign (i.e. '^2+').
+          </xs:documentation>
+        </xs:annotation>
+      </xs:attribute>
       <xs:attribute name="initial" type="xs:string">
         <xs:annotation>
           <xs:documentation>
-            Initial Reaction
+            Initial reaction displayed to students. See the answer attribute for the syntax.
           </xs:documentation>
         </xs:annotation>
       </xs:attribute>
@@ -2509,6 +2524,14 @@
       </xs:documentation>
     </xs:annotation>
     <xs:complexType>
+      <xs:attribute name="id" type="xs:string">
+        <xs:annotation>
+          <xs:documentation>
+            Id that will be part of the HTML input element id.
+            This can be used to get a reference to the input element in Javascript.
+          </xs:documentation>
+        </xs:annotation>
+      </xs:attribute>
       <xs:attribute default="20" name="size" type="int-or-perl">
         <xs:annotation>
           <xs:documentation>
@@ -5485,6 +5508,7 @@
       <xs:sequence>
         <xs:element ref="head"/>
         <xs:element ref="body"/>
+        <xs:element ref="allow" minOccurs="0" maxOccurs="unbounded"/>
       </xs:sequence>
       <xs:attributeGroup ref="i18n"/>
       <xs:attribute name="id" type="xs:ID"/>
@@ -5510,7 +5534,7 @@
     <xs:complexType>
       <xs:sequence>
         <xs:group ref="head.misc"/>
-        <xs:choice>
+        <xs:choice minOccurs="0">
           <xs:sequence>
             <xs:element ref="title"/>
             <xs:group ref="head.misc"/>
@@ -5522,8 +5546,10 @@
           <xs:sequence>
             <xs:element ref="base"/>
             <xs:group ref="head.misc"/>
-            <xs:element ref="title"/>
-            <xs:group ref="head.misc"/>
+            <xs:sequence minOccurs="0">
+              <xs:element ref="title"/>
+              <xs:group ref="head.misc"/>
+            </xs:sequence>
           </xs:sequence>
         </xs:choice>
       </xs:sequence>
@@ -6839,12 +6865,18 @@
       </xs:documentation>
     </xs:annotation>
   </xs:element>
-  <xs:element name="pre" type="inlineBaseType">
+  <xs:element name="pre">
     <xs:annotation>
       <xs:documentation>
         The HTML &lt;pre&gt; Element (or HTML Preformatted Text) represents preformatted text. Text within this element is typically displayed in a non-proportional font exactly as it is laid out in the file. Whitespaces inside this element are displayed as typed.
       </xs:documentation>
     </xs:annotation>
+    <xs:complexType mixed="true">
+      <xs:choice maxOccurs="unbounded" minOccurs="0">
+        <xs:group ref="inlines"/>
+      </xs:choice>
+      <xs:attribute fixed="preserve" ref="xml:space"/>
+    </xs:complexType>
   </xs:element>
   <xs:element name="code" type="inlineBaseType">
     <xs:annotation>