Added 'What is XQuery?' section

Frontend/tools/xquery.html

@@ -21,7 +21,7 @@
         <div id="tool" class="tool rwd-expandable">
             <div class="tool-context">
                 <div class="headline">
-                    <h1>Online XQuery tester</h1>
+                    <h1>Online XQuery Interpreter</h1>
                 </div>
                 <div class="display-space-between">
                     <div style="text-align: center;">
@@ -45,7 +45,7 @@
                     </div>
                 </div>
 
-                <span id="processorTooltipInfo">Supports XQuery up to 3.1</span><br>
+                <span id="processorTooltipInfo">Supports XQuery up to 4.0</span><br>
                 <br>
 
                 <label for="xmlArea"><b>Insert your XML:</b></label>
@@ -71,7 +71,8 @@
         </div>
         <div class="tooltip tooltip-window rwd-hideable">
             <h2>What is XQuery?</h2>
-            TBD
+            <p><b>XQuery</b> (<b>XML Query</b>) is a query and functional programming language that queries and transforms collections of structured and unstructured data, usually in the form of XML, text and with vendor-specific extensions for other data formats (JSON, binary, etc.).</p>
+            <p>Source: <a href="https://en.wikipedia.org/wiki/XQuery">Wikipedia</a></p>
         </div>
 
         <!-- Cut END -->