Fixed #12856 -- Documented BoundField API.

docs/ref/forms/widgets.txt

@@ -230,6 +230,16 @@ foundation for custom widgets.
            In older versions, this attribute was only defined on the date
            and time widgets (as ``False``).
 
+    .. method:: id_for_label(self, id_)
+
+        Returns the HTML ID attribute of this widget for use by a ``<label>``,
+        given the ID of the field. Returns ``None`` if an ID isn't available.
+
+        This hook is necessary because some widgets have multiple HTML
+        elements and, thus, multiple IDs. In that case, this method should
+        return an ID value that corresponds to the first ID in the widget's
+        tags.
+
     .. method:: render(name, value, attrs=None)
 
         Returns HTML for the widget, as a Unicode string. This method must be

docs/topics/forms/index.txt

@@ -690,6 +690,11 @@ Useful attributes on ``{{ field }}`` include:
     :class:`~django.forms.Field` attributes, e.g.
     ``{{ char_field.field.max_length }}``.
 
+.. seealso::
+
+    For a complete list of attributes and methods, see
+    :class:`~django.forms.BoundField`.
+
 Looping over hidden and visible fields
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^