As Joachim says, "Programmers use extensions to _refer_ to a particular feature when talking/writing/searching about it."

I think this is generally important. The language reports provide the foundations for understanding the language and it is important to have a handle to describe the various departures from it -- at least until a new report around which near universal acceptance can be established.

I would extend "2. Restrict the use of more complex features" to say "2. Restrict the use of _novel_ and more complex features". I think many just want to say exactly how they are departing from Haskell 2010, whether those deltas are complex or otherwise.

Chris