obj.onCellDataChanging vs. obj.onCellTextChanging

What is the difference between these two functions?

obj.onCellDataChanging
obj.onCellTextChanging

text - what is visible on the screen
data - what comes from the data source

Often data == text but sometimes you are getting data in one format but want to display them in another. In this case the cell format object is used which transforms data to text (and back).