struggle to use lineoffset

[DVGlasgow at aol.com]

I have a field which following an assessment contains 56 lines, each with 4 
chunks of data and a category identifier  (in word 5).  I want the user to 
click on a line and all (8) of the lines containing data associated from the 
same category to hilite. All 56 lines are unique, so i thought that having 
extracted the category from the selectedline it would be easy to use 
lineoffset to identify all the lines containing the category identifier. 

 But the script below doesn't work.  In fact, it doesn't seem to do anything. 
 Debugging doesn't shed any light on what is going on - at least to me.

on mouseup
  get  the selectedtext of me
  put char 1 to 3 of word 5 of it into tcat
  repeat for each line i in me
    if i contains tcat then select line (lineoffset (i,me)) of me
  end repeat
end mouseup

The field is set up to allow multiple noncontiguous hilited lines.  
Suggestions anyone?

Best wishes,

David Glasgow
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