Document the TrblField

docs/dev/reference/widgets/trbl.md

@@ -1,6 +1,50 @@
 ---
 title: Margins
-description: Four text fields with a small unit drop-down menu (not yet documented)
+description: Four text fields with a small unit drop-down menu.
 ---
 
-{{< widget-notice >}}
+{{% notice "note" %}}
+This widget has been deprecated in Contao **5.7** in favor of the [_Row Wizard_]({{% relref "row-wizard" %}}) widget.
+{{% /notice %}}
+
+This widget renders four text input fields, plus a unit drop-down menu. Its main purpose is to provide the possibility
+to enter margin values (top, right, bottom, left - hence the internal name `trbl`).
+
+![Margins]({{% asset "images/dev/reference/widgets/trbl.png" %}}?classes=shadow)
+
+## Options
+
+This table only shows the options relevant to the core functionality of this widget. See the DCA reference for a
+[full field reference]({{% relref "fields#reference" %}}). All options for the [`text`]({{% relref "text" %}}) widget
+are also relevant.
+
+| Key               | Value                       |
+|-------------------|-----------------------------|---
+| `inputType`       | `trbl` (string)             |
+| `options`         | `array`                     | These are the options available in the unit drop-down. You can also use an [`options_callback`]({{% relref "callbacks#fields-field-options" %}}).
+| `reference`       | `array`                     | Optional translation reference for the drop-down options.
+
+## Column Definition
+
+Typically, a `VARCHAR` field of sufficient length is used, with an `ascii_bin` collation, since this field does not need
+full Unicode support.
+
+## Example
+
+```php
+// …
+'myMargins' => [
+    'label' => ['Margins', 'The margins for this element.'],
+    'inputType' => 'trbl',
+    'options' => 'px', '%', 'em', 'rem',
+    'sql' => [
+        'type' => 'string',
+        'length' => 128,
+        'default' => '',
+        'platformOptions' => [
+            'collation' => 'ascii_bin',
+        ],
+    ],
+],
+// …
+```