XWIKI-18006: Add mechanism to skip header parts and go to main content directly (#1667)

* Add a link to skip header parts and go to main content directly
* Make link visible only when it has focus or when it is active

xwiki-platform-core/xwiki-platform-flamingo/xwiki-platform-flamingo-skin/xwiki-platform-flamingo-skin-resources/src/main/resources/flamingo/edit.vm

@@ -90,6 +90,7 @@
   #template("xwikivars.vm")
   #template("layoutvars.vm")
   #template("htmlheader.vm")
+  #template("skipnav.vm")
   #if($displayMainMenu)
     <div id="menuview">
       #template("menus_view.vm")

xwiki-platform-core/xwiki-platform-flamingo/xwiki-platform-flamingo-skin/xwiki-platform-flamingo-skin-resources/src/main/resources/flamingo/less/layout.less

@@ -362,3 +362,14 @@ already take care of padding and shadow. */
   border-left-color: fade((@xwiki-border-color), 80%);
   border-right-color: fade((@xwiki-border-color), 80%);
 }
+
+.skip-nav {
+  a {
+    position: absolute;
+    top: -20em;
+    z-index: 10;
+    &:focus, &:active {
+      top: 0;
+    }
+  }
+}

xwiki-platform-core/xwiki-platform-flamingo/xwiki-platform-flamingo-skin/xwiki-platform-flamingo-skin-resources/src/main/resources/flamingo/skipnav.vm

+## ---------------------------------------------------------------------------
+## See the NOTICE file distributed with this work for additional
+## information regarding copyright ownership.
+##
+## This is free software; you can redistribute it and/or modify it
+## under the terms of the GNU Lesser General Public License as
+## published by the Free Software Foundation; either version 2.1 of
+## the License, or (at your option) any later version.
+##
+## This software is distributed in the hope that it will be useful,
+## but WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+## Lesser General Public License for more details.
+##
+## You should have received a copy of the GNU Lesser General Public
+## License along with this software; if not, write to the Free
+## Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
+## 02110-1301 USA, or see the FSF site: http://www.fsf.org.
+## ---------------------------------------------------------------------------
+## Provide a way to skip directly to the main content of page
+## See: https://www.w3.org/TR/WCAG20-TECHS/G1.html
+<div class="skip-nav">
+  #if ("$!xcontext.action" == 'view' || "$!xcontext.action" == 'preview')
+    ## Point at #xwikicontent to skip over the navigation tools including the breadrumb
+    #set ($targetNav = '#xwikicontent')
+  #elseif (("$!xcontext.action" == 'inline' || "$!xcontext.action" == 'edit') && !$editConfirmation)
+    ## In edit mode, point at the title field
+    #set ($targetNav = '#editMeta')
+  #else
+    ## Point at '#mainContentArea' which is present in all pages that include "startpage.vm"
+    #set ($targetNav = '#mainContentArea')
+  #end
+  <a class="btn btn-default" href="$targetNav">$services.localization.render('skin.skipnav.links.content.title')</a>
+</div>

xwiki-platform-core/xwiki-platform-flamingo/xwiki-platform-flamingo-skin/xwiki-platform-flamingo-skin-resources/src/main/resources/flamingo/startpage.vm

@@ -20,6 +20,7 @@
 #template("xwikivars.vm")
 #template("layoutvars.vm")
 #template("htmlheader.vm")
+#template("skipnav.vm")
 #if($displayMainMenu)
   <div id="menuview">
     #template("menus_view.vm")

xwiki-platform-core/xwiki-platform-oldcore/src/main/resources/ApplicationResources.properties

@@ -342,6 +342,9 @@ platform.core.editConfirmation.errors=Editing is forbidden for the reasons liste
 platform.core.editConfirmation.warnings=Editing can be forced, but be aware of the warnings below.
 platform.core.editConfirmation.additionalWarnings=In addition to the errors listed above, the warnings below have also been identified.
 
+### Skip to
+skin.skipnav.links.content.title=Skip to Content
+
 ###
 ### Model
 ###