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Description of problem:
undocumented option '-y' and '+N -N' (N is a number) for position arguments

Version-Release number of selected component (if applicable):
coreutils-8.4-19.el6_4.2.x86_64

How reproducible:
always

Steps to Reproduce:
1. `touch file`
2. `sort -y file`

Actual results:
empty output

Expected results:
either:
sort: invalid option -- 'y'
Try `sort --help' for more information.
or better have it documented

Additional info:
please see bug 956143 where support for +N -N was added, these are not documented neither.

+N -N is intentionally undocumented - it is mentioned it is OBSOLETE format - thus is not recommended/mentioned on the manpage/info page. Still taken, but not documented. Regression was with wrong function, not with this format.
-y option is the same - accepted but ignored and not recommended - just for compatibility with Solaris.

Closing NOTABUG, I don't see any sense to add them to man/info documentation, as these are obsolete/compat options.