Great suggestion, thanks!

Released in 2.5

Released in 2.0

Yes, I agree that it's subtle. But it is so to avoid creating visual noise. Please also notice that these icons change when you scroll the text using Left-Right buttons (or with Left Click + Scroll). 

Thanks for pointing out that this is not described in help. Of course it should be there, I'll add the description of this behavior.

But there is already one:

Fixed in 2.6.1