Autoselect input in markup dialog

Some code inspiration from @WouterDS.

See #371.

try.html

@@ -733,6 +733,8 @@ is where the current server got started.
 
 <script>
 // Search
+//
+
 var searchBadgeDb = {index: [], tr: []};
 function searchBadgeDbInit() {
   searchBadgeDb = {index: [], tr: []};
@@ -765,6 +767,8 @@ function searchBadge(event) {
 document.addEventListener('DOMContentLoaded', searchBadgeDbInit);
 
 // Suggested badges search
+//
+
 function isUrl(url) {
   var http = url.slice(0, 5) === 'http:';
   var https = url.slice(0, 6) === 'https:';
@@ -806,8 +810,32 @@ function suggestBadgeInit() {
 
 document.addEventListener('DOMContentLoaded', suggestBadgeInit);
 
+// Auto-select code snippets
+//
+
+// Select and highlight the node's textual content.
+// Use this as an event listener.
+function selectNode(e) {
+  if (e.target.select) {
+    e.target.select();
+  } else {
+    if (document.selection) {
+      var range = document.body.createTextRange();
+      range.moveToElementText(e.target);
+      range.select();
+    } else if (window.getSelection) {
+      var range = document.createRange();
+      range.selectNode(e.target);
+      window.getSelection().addRange(range);
+    }
+  }
+};
+copyMarkdown.addEventListener('click', selectNode);
+copyreStructuredText.addEventListener('click', selectNode);
 
 // Markup copier dialog
+//
+
 function markupDialogInit() {
   var trs = document.querySelectorAll('table.badge tr');
   for (var i = 0; i < trs.length; i++) {
@@ -884,7 +912,10 @@ copyForm.addEventListener('click', function(event) {
   event.stopPropagation();
 });
 
+
 // Custom badge
+//
+
 function makeImage() {
   var url = document.getElementById('imgUrlPrefix').textContent;
   url += escapeField(imageMaker.subject.value);
@@ -900,6 +931,8 @@ function escapeField(s) {
 
 
 // Convert object literal to xhr-sendable.
+//
+
 function toXhrSend(data) {
   var str = '', start = true;
   var jsondata = '';