Stocks and currencies

[Alpar Juttner]

Here is some stupid questions of a new gnucash user.
I apologize, if they have already been discussed.

1. What is the standard gnucash file extension? Sometimes '.xac' is 
used, but I found it nowhere explicitly mentioned.
2. Stock accounts have no "currency" in gnucash-1.8.7 (like the
"security" was in gnucash-1.6.x). How to handle stocks with other than
the default currency?
3. I don't understand 'stock accounts' at all. Please take a look at the
gnucash file http://www.cs.elte.hu/~alpar/gnucash/stock.xac for a
moment. In this example I started with $100,000 cash, then bought 1000
shares from XYZ for $20,000, and later sold them for $30,000. Now I have
$110,000 assets with 0 shares. But there is a hidden imbalance here,
isn't there? I would like to see this $10,000 on an income account. What
is the legal way to do that? See the other file
http://www.cs.elte.hu/~alpar/gnucash/stock-corr.xac . This is almost
right, but it is really a hacking. It seems to me that a stock account
should count the number of shares _as_well_as_ the "value" of the
transactions, and special transactions should be enabled that have an
effect _only_ on the "value balance" (it is not yet enabled as far as I
see, I had to "emulate" it by buying for extremely high price in the
second example.)

Thank you in advance for your help.

Alpar