Inserting unicodeText into a unicode string? #3

[Richmond]

  "Oh, Dear, Richmond's on a roll . . . ."

So; the story so far:

Richmond has worked out how to shove unicodeText inside other unicodeText:

on mouseUp
     set the useUnicode to true
     set the unicodeText of the selectedText to numToChar(50000)
end mouseUp


But, now, being one of those types who always wants more, he wants to
check what the unicode Char precedes the insertion point . . .

Tried:

on mouseUp
    set the useUnicode to true
    if the unicodeText of the selectedText -1 = numToChar(32) then
       set the unicodeText of the selectedText to numToChar(50000)
    else
       set the unicodeText of the selectedText to numToChar(60000)
       end if
end mouseUp

which, bye-the-bye, the script-editor said was acceptable . . .

[ quite WHY I thought of '-1' is hard to explain ]

but no good at all . . .  :(