Inserting unicodeText into a unicode string? #2

[Richmond]

  Imagine a field "fTX" that contains the text 'meaty chunks';
when I click between 'meaty' and 'chunks' I want to be
able to insert something there via code rather than via keyboard.

So, why does this not work; in the script of fld "fTX" ?

on mouseUp
   select the text of me
end mouseUp

i.e. the text in fld "fTX" is not selected.

Now:

1. How can I get to a situation where when I click in a textField 
containing text I get this:

1.1. the part of the string in the field before the place where I click 
(or move my cursor) is selected
       and put into another field (e.g. 'fBEFORE') and the part of the 
string after the place where I click
      (or move my cursor) is selcted and put into another field (e.g. 
'fAFTER')?

1.2. allowing me to INSERT text programmtically between the 2 chunks of 
the string.

Something tells me (I dunno what) that I am not being screamingly 
original and this must be:

2.1. Documented somewhere.

2.2. Have been done many, many times before.

2.3. I am just being 'plain stooopid'.

Richmond.