Clarification on Triggers upon delete operation

Hi Team,

We have a requirement where, when an additional identifier is deleted, we need to validate whether it has an expiration date populated. If the expiration date is missing while deleting, we should display a validation error stating: "Expiration date should be populated before deleting an additional identifier."\

I understand that we may need to implement a script in the 'Before Remove' event. However, I am not certain which specific function or method should be used to handle the delete operation

Could you please advise:

• Which function or method should be used to implement this in groovy?
• How can I efficiently iterate through all additional identifier and write a groovy script to resolve this?