Attaching patch which prints default value in explain and description.
defaultVal is allowed to be null, and in that case it defaults to the x (source) value. In this patch I explicitly print the source value in that case. An alternative could be to omit default value and print only map(x,min,max,target) as today.
Shalin Shekhar Mangar, you have been involved in this class before, what is your opinion?