Analytic Function bug?

Last Tuesday we had an ODTUG Preview mini-conference at our office in Nieuwegein, The Netherlands. Nine presentations with nine fine speakers. Too bad the session were in parallel, and thus you had to pick and choose which session to attend. Oh well, that's always the case with conferences, even tiny ones like this one.
Because I'm doing a presentation during the ODTUG Kaleidoscope 2010, I also did my presentation last Tuesday.
The feedback I got was good, and I also got some pointers to make the presentation better.

While changing one of the demo's, I rediscovered of what I believe to be a documentation bug. The demo is about showing the Windowing Clause with Analytic Functions. If you are not familiar with Analytic Functions, attend my session and you will know all about it... ;)
Anyway, to create a running total using the EMP table use the SUM with the default Windowing Clause and you're good to go. You would have to know what the default Windowing Clause is in that case.
The documentation states

If you omit the windowing_clause entirely, then the default is RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW.

Let's go back to the example, a running total on Scott's EMP table

SQL> select ename
  2       , sal
  3       , sum (sal) over (order by ename) running_total
  4    from emp
  5   where deptno = 20
  6   order by ename
  7  ;
 
ENAME            SAL RUNNING_TOTAL
---------- --------- -------------
ADAMS           1100          1100
FORD            3000          4100
JONES           2975          7075
SCOTT           3000         10075
SMITH            800         10875

Because we omitted the Windowing Clause, we get the Default - range between unbounded preceding and current row.
Being explicit about the Windowing Clause, we get the same results - just as we expect.

SQL> select ename
  2       , sal
  3       , sum (sal) over (order by ename
  4                         range between unbounded preceding
  5                                   and current row
  6                        ) running_total
  7    from emp
  8   where deptno = 20
  9   order by ename
 10  ;
 
ENAME            SAL RUNNING_TOTAL
---------- --------- -------------
ADAMS           1100          1100
FORD            3000          4100
JONES           2975          7075
SCOTT           3000         10075
SMITH            800         10875

And the short notation of the Default Windowing Clause also yields the same results

SQL> select ename
  2       , sal
  3       , sum (sal) over (order by ename
  4                         range unbounded preceding
  5                        ) running_total
  6    from emp
  7   where deptno = 20
  8   order by ename
  9  ;
 
ENAME            SAL RUNNING_TOTAL
---------- --------- -------------
ADAMS           1100          1100
FORD            3000          4100
JONES           2975          7075
SCOTT           3000         10075
SMITH            800         10875

Why do I believe this to be a bug because of the definition of a Range Window.

RANGE specifies the window as a logical offset.

and this part:

• If value_expr evaluates to a numeric value, then the ORDER BY expr must be a numeric or DATE data type.


• If value_expr evaluates to an interval value, then the ORDER BY expr must be a DATE data type

Look back at the examples and notice that I didn't use a Numeric or DATE data type in the ORDER BY expression - I used a VARCHAR2 (ename is after all a VARCHAR2). And this is in contradiction with the documentation quotes from above.
Using the Range Window - not the Default one - with the ename column raises an exception

SQL> select ename
  2       , sal
  3       , sum (sal) over (order by ename
  4                         range between 400 preceding
  5                                   and 400 following
  6                         ) running_total
  7    from emp
  8   where deptno = 20
  9   order by sal
 10  /
 
select ename
     , sal
     , sum (sal) over (order by ename
                       range between 400 preceding
                                 and 400 following
                       ) running_total
  from emp
 where deptno = 20
 order by sal
 
ORA-00902: invalid datatype

I believe the Default Windowing Clause should be

rows between unbounded preceding and current row

And to use the Default Windowing explicitly would show this:

SQL> select ename
  2       , sal
  3       , sum (sal) over (order by ename
  4                         rows between unbounded preceding
  5                                   and current row -- Should be the default Window Clause
  6                        ) running_total
  7    from emp
  8   where deptno = 20
  9   order by ename
 10  ;
 
ENAME            SAL RUNNING_TOTAL
---------- --------- -------------
ADAMS           1100          1100
FORD            3000          4100
JONES           2975          7075
SCOTT           3000         10075
SMITH            800         10875

Maybe, probably, I misinterpret the Oracle Documentation. If you believe the Oracle Documentation is correct, can you try and explain it to me?
I did make a note of it in the Oracle Documentation, you can add user comments, but it never made it past the moderators... I guess they don't agree with me. ;)
Links
Oracle Documentation on Analytic Functions