In QGIS 2.16 the expression engine now supports use of named parameters. This means that instead of writing the cryptic expression:
clamp(1,2,3)
you can use:
clamp( min:=1, value:=2, max:=3)
This change also allows arguments to be switched, eg:
clamp( value:=2, max:=3, min:=1)
Using named parameters helps clarify what the arguments for an expression function refer to, which is helpful when you are trying to interpret an expression at a later date!
This feature was developed by Nyall Dawson (North Road)