[Coco] What are the rules for naming basic09 variables ?

[coco at jechar.ca]

  I have seen examples of variable names 10 or 11 characters long and of 
the $ being used in a
  variable name.

  So I know that alpha numeric and $ are legal components and at least 10 
characters long but I cannot
  find the explicit rules so for example is underscore a legal variable 
name component, what is the
  maximum number of characters  in a variable and are they all used or 
for example would
  VARIABLE1 be the same as VARIABLE2 because first eight characters are 
all the same ?

  Only answer what you know for sure. I could always try writing a bunch 
of test programs to
  come up with the rules experimentally but perhaps someone knows the 
exact restrictions on basic09
  variable naming ?

  Charles