A little hack to show file fields only for specific file types. Should also work for almost every custom field.

To install the plugin, please put it in the site/plugins directory.
The plugin folder must be named file-types.

site/plugins/
    file-types/
        file-types.php
        ...

You can now use the fileType attribute in the field declarations.

# site/blueprints/fields/meta.yml

type: group
fields:

  label:
    label: Label
    type: text
    required: true
    fileType:
      - document
      - archive

  focus:
    label: Focus
    type: focus
    fileType: image