The order.item object contains information held against an opportunity Item record. Theorder.item object can be accessed in opportunity document layouts: 

{% for item in order.items %}
  {{ item.name }}
{% endfor %}

It may also be accessed in the product_assets or container_item_assets loop:

{% for asset in order.product_assets %}
  {{ asset.opportunity_item.name }}
{% endfor %}

Objects

View a list of objects on Google Sheets

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