The expand action allows you to add new fields to an item being processed, as well as preserve the order of the existing fields. It takes a single argument, set, which is a dictionary of field-value pairs to be added to the item.

Here’s an example of how you might use the expand action in a YAML file:

actions:
  add_mandatory_columns:
    action: expand
    set:
      code: ''
      attributes: []
      filters: []
      sortorder: []
      attribute_as_image: ''
      attribute_as_label: 'Title'
      default_metric_units: ''
      attribute_filters_filter: []
      attribute_filters_internal: []
      requirements-ecommerce: []

In this example, the expand action will add the specified fields and values to the item being processed. If any of the fields already exist in the item, their values will not be overridden.