What does the value 5874897 AD mean? Which year, month, day, please?

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/11/datatype-datetime.html
Description:

See also
https://stackoverflow.com/questions/29434748/what-does-bc-date-mean-in-postgresql.

Add a note about how the date/timestamp is internally represented, please.
E.g.
https://docs.teradata.com/reader/S0Fw2AVH8ff3MDA0wDOHlQ/dkWLOva_L12uKvSnUcJQsQ.