[ADD] support for generic alternative content in right-hand side

dd.alternatives triggers "widget", each (dt, dd) is an alternative with
dt being the alternative (and radio button) label and dd being the
actual content to display on selection.

_static/accounting.css

@@ -153,3 +153,17 @@ blockquote.highlights {
     margin-bottom: 0;
     text-align: center;
 }
+
+/*
+  lists of alternatives
+*/
+.alternatives-controls label {
+    display: block;
+}
+dl.alternatives > dt,
+dl.alternatives > dd {
+    display: none;
+}
+dl.alternatives > dd {
+    margin-left: 0;
+}

_static/misc.js

@@ -1,5 +1,52 @@
 (function () {
     document.addEventListener('DOMContentLoaded', function () {
+        alternatives()
+        checks_handling();
+    });
+
+    /** alternatives display:
+     *  - prepend control for each <dt>
+     *    - radio input with link to following dd
+     *    - label is <dt> content
+     *    - hide all first-level dt and dd (CSS)
+     *  - on change
+     *    - hide all dds
+     *    - show dd corresponding to the selected radio
+     *  - automatically select first control on startup
+     */
+    function alternatives() {
+        $('dl.alternatives').each(function (index) {
+            var $list = $(this),
+                $contents = $list.children('dd');
+            var $controls = $('<div class="alternatives-controls">').append(
+                $list.children('dt').map(function () {
+                    var label = document.createElement('label'),
+                        input = document.createElement('input');
+                    input.setAttribute('type', 'radio');
+                    input.setAttribute('name', 'alternatives-' + index);
+
+                    var sibling = this;
+                    while ((sibling = sibling.nextSibling) && sibling.nodeType !== 1);
+                    input.content = sibling;
+
+                    label.appendChild(input);
+                    label.appendChild(document.createTextNode(' '));
+                    label.appendChild(document.createTextNode(this.textContent));
+
+                    return label;
+                }))
+                .insertBefore($list)
+                .on('change', 'input', function (e) {
+                    // change event triggers only on newly selected input, not
+                    // on the one being deselected
+                    $contents.css('display', '');
+                    var content = e.target.content;
+                    content && (content.style.display = 'block');
+                })
+                .find('input:first').click();
+        });
+    }
+    function checks_handling() {
         var $section = $('.checks-handling');
         if (!$section.length) { return; }
 
@@ -9,7 +56,7 @@
                 while (this.firstChild) {
                     this.removeChild(this.firstChild)
                 }
-                
+
                 $('<label style="display: block;">')
                     .append('<input type="radio" name="checks-handling">')
                     .append(' ')
@@ -28,5 +75,6 @@
             }).eq(idx).prop('checked', true);
             $ul.nextAll('div').hide().eq(idx).show();
         }
-    });
+
+    }
 })();