XCOMMONS-901: Support both XHTML 1.0 and XHTML 5 in HtmlCleaner

* Document another exception in BodyFilter
* Improve robustness in HTML version parameter parsing

xwiki-commons-core/xwiki-commons-xml/src/main/java/org/xwiki/xml/internal/html/DefaultHTMLCleaner.java

@@ -318,8 +318,8 @@ private int getHTMLVersion(HTMLCleanerConfiguration configuration)
     {
         String param = configuration.getParameters().get(HTMLCleanerConfiguration.HTML_VERSION);
         int htmlVersion = 4;
-        if (param != null) {
-            htmlVersion = Integer.parseInt(param);
+        if ("5".equals(param)) {
+            htmlVersion = 5;
         }
         return htmlVersion;
     }

xwiki-commons-core/xwiki-commons-xml/src/main/java/org/xwiki/xml/internal/html/filter/BodyFilter.java

@@ -57,7 +57,8 @@ public class BodyFilter extends AbstractHTMLFilter
      * }</pre>
      *
      * We also use this list for HTML5 where in theory everything is allowed, but we instead only allow flow content
-     * that is not also phrasing content except for {@code <ins>} and {@code <del>} that were already allowed in HTML 4.
+     * that is not also phrasing content except for {@code <ins>} and {@code <del>} that were already allowed in HTML
+     * 4 and {@code <template>} which is not rendered and thus no extra paragraph should be created for it.
      */
     private static final List<String> ALLOWED_BODY_TAGS = Arrays.asList(HTMLConstants.TAG_ADDRESS,
         HTMLConstants.TAG_ARTICLE, HTMLConstants.TAG_ASIDE, HTMLConstants.TAG_BLOCKQUOTE, HTMLConstants.TAG_DEL,