Use of entity_extract_ids($entity_type, $entity)
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I am trying to use entity_extract_ids($entity_type, $entity) where:

**$entity_type** = The entity type; e.g. 'node' or 'user'.

**$entity** = The entity from which to extract values.

I have never used this function and don't understand what the second parameter (i.e. **$entity**) is supposed to be.

I would love to see an example code with this function being used. Thank you.