Using advance update

Dear Milist,
Somebody please give me more explanation about
using "Update" syntax with cursor. I've seen this
on manual of postgre(sql-update.html). Here it is
the example;

UPDATE table SET column = expression [, ...]
WHERE CURRENT OF cursor

But there's no further clearly explanation or the
sample of usages. Somebody please give me ones.

Thank's and GOD Bless You.

Yudha Setiawan.
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