number as a fist letter of custom property. Allowed or not?

[Tariel Gogoberidze]

When you are trying to manually enter  a  number as a custom property
name, MC returns the message "A custom property name must start with a letter"

However when  you  are trying to do the same  through  script it works fine

on mouseup
  put "128"  into tTest
  set the tTest of fld 1 to "some content" -- works
end mouseup

 Another exampleи

on mouseUp
  repeat with j= 1 to 10
    repeat with i= 1 to 10
      put "Content of Cell" &&j&","&i  into SheetArray[j,i]
    end repeat
  end repeat
  ##
  -- this works  as it  supposed to
  -- set the customProperties["SheetData"] of  fld 1 to SheetArray
  -- put the SheetData ["7,2"] of fld 1
  ##
  -- but  why this works if custom property name MUST start with a letter?
  set the customProperties of fld 1 to SheetArray
  put "5,3" into tTemp
  put the tTemp of fld 1
##
end mouseup

So is it allowed to use a  number as a fist letter of custom property or not?

Best regards,
Tariel Gogoberidze