[TIP] tox environment separation docs

[anatoly techtonik]

Hi,

Where are the docs or spec that describe how tox
separates working directory and its virtualenv?

https://testrun.org/tox/latest/#what-is-tox

When I redirect output to file in this PR [1], the file
is created in my project root and not in virtualenv
working directory. So I'd like to read some spec to
understand what this working directory should be.

1. https://bitbucket.org/hpk42/tox/pull-requests/206/support-piping-command-output-to-file/diff

-- 
anatoly t.