Add an optional off value to Doku_Form’s checkboxes

Since an unchecked HTML checkbox has no value at all, a hidden field may be
used to specify an off value for the checkbox.

inc/form.php

@@ -484,6 +484,8 @@ function form_makeFileField($name, $label=null, $id='', $class='', $attrs=array(
  * form_makeCheckboxField
  *
  * Create a form element for a checkbox input element with label.
+ * If $value is an array, a hidden field with the same name and the value
+ * $value[1] is constructed as well.
  *
  * @see     form_makeFieldRight
  * @author  Tom N Harris <tnharris@whoopdedo.org>
@@ -818,6 +820,8 @@ function form_filefield($attrs) {
  *   _class : class attribute used on the label tag
  *   _text  : Text to display after the input. Not escaped.
  * Other attributes are passed to buildAttributes() for the input tag.
+ * If value is an array, a hidden field with the same name and the value
+ * $attrs['value'][1] is constructed as well.
  *
  * @author  Tom N Harris <tnharris@whoopdedo.org>
  */
@@ -827,7 +831,13 @@ function form_checkboxfield($attrs) {
     $s = '<label';
     if ($attrs['_class']) $s .= ' class="'.$attrs['_class'].'"';
     if (!empty($attrs['id'])) $s .= ' for="'.$attrs['id'].'"';
-    $s .= '><input type="checkbox" '.buildAttributes($attrs,true).'/>';
+    $s .= '>';
+    if (is_array($attrs['value'])) {
+        echo '<input type="hidden" name="' . hsc($attrs['name']) .'"'
+                 . ' value="' . hsc($attrs['value'][1]) . '" />';
+        $attrs['value'] = $attrs['value'][0];
+    }
+    $s .= '<input type="checkbox" '.buildAttributes($attrs,true).'/>';
     $s .= ' <span>'.$attrs['_text'].'</span></label>';
     if (preg_match('/(^| )block($| )/', $attrs['_class']))
         $s .= '<br />';