silly text editing question

[Mark Smith]

How do you find out where the current "insertion point" in an  
editable field is?

I mean, if you have:

This is line 1
This is line 2
This is line 3

in an editable field, if the user has placed the caret after the 'n'  
in line 2 and then hit return for example, how do you know where in  
the field you are? (either in terms of chars, or char n of line n, or  
whatever).

This is probably really simple, but I can't for the life of me figure  
it out!

Best,

Mark