to_number function questions

What does to_number do with a string like "123x78" ?  Does
it try to convert the whole string?  Does it stop at x, giving 123?
Does it drop x?  Does it return some sort of failure?

Also, suppose that you give to_number 123, and the second parameter is
"999999" ?  Do the extra 9's give any problem (you dn't always know
whether to_number will get 0-99999, so what do you give it in the
formatting string?  If it has more 9's in the format string than are
digits in the number, will it pad it?

Sorry for all the q's but the page
http://www.postgresql.org/idocs/index.php?functions-formatting.html
only lists things in tables and does not discuss the sorts of questions
or oddball inputs/exceptions I ask about.

Thanks,
--Cindy
--
ctmoore@uci.edu