Is there a document or help file that shows ALL available Placeholders that can be used in the email templates?

We have found that there are additional Placeholders that can be used in templates that are not listed in the Placeholders list.

For example in the Purchase Order email template there is no placeholder for Terms and Conditions but, you can use %PO_TermsAndCondition% to bring it up.

We need to use the "Shipment Preference" but that is not an available placeholder, it will be great if Zoho provides a document that show all the placeholder available, thanks