MINOR Cross-referencing some documentation (from r108375)

git-svn-id: svn://svn.silverstripe.com/silverstripe/open/modules/sapphire/trunk@112721 467b73ca-7a2a-4603-9d3b-597d59a354a9

forms/DropdownField.php

@@ -68,6 +68,10 @@
  * );
  * </code>
  * 
+ * @see CheckboxSetField for multiple selections through checkboxes instead.
+ * @see ListboxField for a single <select> box (with single or multiple selections).
+ * @see TreeDropdownField for a rich and customizeable UI that can visualize a tree of selectable elements
+ * 
  * @package forms
  * @subpackage fields-basic
  */

forms/ListboxField.php

@@ -17,6 +17,11 @@
  * )
  * </code> 
  * 
+ * @see DropdownField for a simple <select> field with a single element.
+ * @see CheckboxSetField for multiple selections through checkboxes.
+ * @see OptionsetField for single selections via radiobuttons.
+ * @see TreeDropdownField for a rich and customizeable UI that can visualize a tree of selectable elements
+ * 
  * @package forms
  * @subpackage fields-basic
  */

forms/OptionsetField.php

@@ -47,6 +47,10 @@
  * // Pass the fields to the form constructor. etc
  * </code>
  * 
+ * @see CheckboxSetField for multiple selections through checkboxes instead.
+ * @see DropdownField for a simple <select> field with a single element.
+ * @see TreeDropdownField for a rich and customizeable UI that can visualize a tree of selectable elements
+ * 
  * @package forms
  * @subpackage fields-basic
  */

forms/TreeDropdownField.php

@@ -23,6 +23,11 @@
  * </code>
  * 
  * This will generate a tree allowing the user to expand and contract subsections to find the appropriate page to save to the field.
+ * 
+ * @see TreeMultiselectField for the same implementation allowing multiple selections
+ * @see DropdownField for a simple <select> field with a single element.
+ * @see CheckboxSetField for multiple selections through checkboxes.
+ * @see OptionsetField for single selections via radiobuttons.
  *
  * @package forms
  * @subpackage fields-relational

forms/TreeMultiselectField.php

@@ -30,6 +30,8 @@
  * }
  * </code> 
  * 
+ * @see TreeDropdownField for the sample implementation, but only allowing single selects
+ * 
  * @package forms
  * @subpackage fields-relational
  */