get the index of a word in a textFrame

[Scubilion]

Hello,
First, I'm french user of Indesign CS3, so excuse me for my bad english.
I'd like to get the index of a word in a textFrame when the selection is an insertion point that is placed in a word. I tried this in javascript (I suppose there is a textFrame that containts some texts):
var mySelection = app.selection[0]
if (mySelection.constructor.name = "insertionPoint"){
SelIndex = mySelection.words[0].index}
SelIndex give me the index of the insertionPoint, but not the index of the word in which the insertionPoint is.
What happen ?
I'd like to get the index of the word in the textFrame or the Story.
Thanks for your help.
Fr. Scubilion