diff --git a/complete.html b/complete.html
index 5baa61a735a..311a4bfdf71 100644
--- a/complete.html
+++ b/complete.html
@@ -9265,6 +9265,15 @@ <h4 id=global-attributes><span class=secno>3.2.3 </span><dfn>Global attributes</
   actually have an <code title="">xmlns</code> attribute in no
   namespace specified.</p>
 
+  <hr><p>The XML specification also allows the use of the <code title=attr-xml-space>xml:space</code> attribute in the <a href=#xml-namespace>XML
+  namespace</a> on any element in an <a href=#xml-documents title="XML
+  documents">XML document</a>. This attribute has no effect on
+  <a href=#html-elements>HTML elements</a>, as the default behavior in HTML is to
+  preserve whitespace. <a href=#refsXML>[XML]</a></p>
+
+  <p class=note>There is no way to serialize the <code title=attr-xml-space>xml:space</code> attribute on <a href=#html-elements>HTML
+  elements</a> in the <code><a href=#text/html>text/html</a></code> syntax.</p>
+
   <hr><p>To enable assistive technology products to expose a more
   fine-grained interface than is otherwise possible with HTML elements
   and attributes, a set of <a href=#annotations-for-assistive-technology-products-(aria)>annotations for assistive technology
diff --git a/index b/index
index 90b1dcb4aae..7b009559023 100644
--- a/index
+++ b/index
@@ -9242,6 +9242,15 @@ interface <dfn id=htmlunknownelement>HTMLUnknownElement</dfn> : <a href=#htmlele
   actually have an <code title="">xmlns</code> attribute in no
   namespace specified.</p>
 
+  <hr><p>The XML specification also allows the use of the <code title=attr-xml-space>xml:space</code> attribute in the <a href=#xml-namespace>XML
+  namespace</a> on any element in an <a href=#xml-documents title="XML
+  documents">XML document</a>. This attribute has no effect on
+  <a href=#html-elements>HTML elements</a>, as the default behavior in HTML is to
+  preserve whitespace. <a href=#refsXML>[XML]</a></p>
+
+  <p class=note>There is no way to serialize the <code title=attr-xml-space>xml:space</code> attribute on <a href=#html-elements>HTML
+  elements</a> in the <code><a href=#text/html>text/html</a></code> syntax.</p>
+
   <hr><p>To enable assistive technology products to expose a more
   fine-grained interface than is otherwise possible with HTML elements
   and attributes, a set of <a href=#annotations-for-assistive-technology-products-(aria)>annotations for assistive technology
diff --git a/source b/source
index 9a185ca5edb..567b40f9ea3 100644
--- a/source
+++ b/source
@@ -9351,6 +9351,19 @@ interface <dfn>HTMLUnknownElement</dfn> : <span>HTMLElement</span> { };</pre>
 
   <hr>
 
+  <p>The XML specification also allows the use of the <code
+  title="attr-xml-space">xml:space</code> attribute in the <span>XML
+  namespace</span> on any element in an <span title="XML
+  documents">XML document</span>. This attribute has no effect on
+  <span>HTML elements</span>, as the default behavior in HTML is to
+  preserve whitespace. <a href="#refsXML">[XML]</a></p>
+
+  <p class="note">There is no way to serialize the <code
+  title="attr-xml-space">xml:space</code> attribute on <span>HTML
+  elements</span> in the <code>text/html</code> syntax.</p>
+
+  <hr>
+
   <p>To enable assistive technology products to expose a more
   fine-grained interface than is otherwise possible with HTML elements
   and attributes, a set of <span>annotations for assistive technology