Clarification on validating data on more than one field?

Can anyone shine light on this one, maybe a basic question but just want to know what it is actually doing?

When you validate data on more than one field what is it actually doing?

For example both these fields are in the same table.

validate data1086×942 93.9 KB

Checks two fields to see if the data already exists, but is this actually doing it independently for each field.

‘validate_email’
‘validate_account’

Or is it: ‘validate_email’ OR ‘validate_account’

Or is it" validate_email’ AND ‘validate_account’

Many thanks!