AT&T 6300 Programmer's Manual page 234

DIM
Statement
Syntax
array
subscripts
Remarks
7-78
Specifies the array name, the number of
dimensions and the subscript upper bound per
dimension. The DIM statement may specify
one or more arrays.
DIM array (subscripts)[,array
(subscripts)] ...
is a valid array name. Any legal variable name may be used.
refers to one or more numeric expressions which specify the
array dimensions. Each subscript must be separated from
the next by commas. The number of subscripts specifies the
number of dimensions, and the value of each specifies the
subscript upper bound.
If an array name is used without a
corresponding DIM statement, the maximum
value of the array's subscript(s) defaults to 10.
If a subscript is used that is greater than the
maximum specified, a "Subscript out of range"
error occurs. The minimum value for a
subscript is always 0, unless otherwise
specified with the OPTION BASE statement.
If no D1M is specified, the first reference to an
array element in the program will create the
array with the specified number of
dimensions. For example, if a program
statement refers to: AR1(3,5,10) then AR1 is
created with 3 dimensions and a default upper
bound of 10 for each dimension.