# Custom Data

The `sleekPixel/data/custom` filter adds entries to the **Custom** group of
the editor's [dynamic data](/docs/pixel/dynamic-data.md). Each entry is an array
with three keys:

- `value`: the entry's ID. In a text or an image source it is used as
  `{custom.<value>}`.
- `label`: the name the editor lists it under.
- `data`: the text the image shows. Return a string.

The first entry below reads the ACF field `subtitle` of the post the image is
rendered for; the second is a fixed text.

```php
add_filter('sleekPixel/data/custom', function ($entries, $args) {
  $postId = (int) ($args['postId'] ?? 0);
  $subtitle = $postId ? get_field('subtitle', $postId) : '';

  $entries[] = [
    'value' => 'subtitle',
    'label' => 'Subtitle',
    'data' => is_string($subtitle) ? $subtitle : '',
  ];

  $entries[] = [
    'value' => 'campaign',
    'label' => 'Campaign line',
    'data' => 'Summer sale: 20% off',
  ];

  return $entries;
}, 10, 2);
```

## When the filter runs

- **When the editor loads**, to build its list, with `postId` set to `0`. Only
  `value` and `label` matter here.
- **When an image renders**, with the post's ID in `postId`. One of these calls
  also passes the design's `settings`, `elements`, `other` and `locations`, so
  `data` can depend on both the post and the image.

When an image renders, an entry without a `value`, a `label` or a `data`, or
whose `data` is `null`, is left out, and its placeholder renders as empty text.
Return an empty string rather than `null` when a post has no value; a function
such as `get_field()` returns `null` for a missing field.

The filter's parameters are in the [hooks reference](/docs/pixel/reference/hooks.md).