/usr/share/doc/postgresql-doc-9.3/contrib/README.xor_aggregate is in postgresql-comparator 2.2.2-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 | provide xor-aggregate function for INT2, INT4, INT8 and BIT types.
load with:
sh> psql < <path-to-postgresql>/share/contrib/xor_aggregate.sql
use as:
pgsql> SELECT ..., XOR(column_name) FROM ... GROUP BY ...;
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