“Exclude prefix/suffix” validation is applied to data before/after what matches the Data Identifier Pattern.
“Exclude beginning/ending character” validation is applied to data that matches the Data Identifier Pattern.

Example:
Data Identifier Pattern: \d{3.EN_US}-\d{2.EN_US}-\d{4.EN_US}
Message: “This is some text with number <example_identifier>  with no reference.”

If DI pattern matches with - “<example_identifier>”
Exclude suffix validation applied to data that follows the actual match i.e. “with no reference.”
Exclude ending character validation applied to data that matches the pattern i.e. “example_identifier”

Same is the case with exclude beginning character and exclude prefix.

More information about validator can be found in documentation here - Using optional validators (broadcom.com)