Programmatically find whether installing from unknown sources is allowed

Question

I need to find whether the current Android device allows to install apps from sources other than the market. This option appears in the settings UI under Applications named

Answer 1

This setting is called "INSTALL_NON_MARKET_APP" (click for documentation).

(I basically already typed the question when I found the answer hidden deep within documentation, with a different name, so I decided to post the question and self answer, since it's not trivial.)