AT&T 6300 Programmer's Manual page 212

COMMON
Statement
Syntax
variable
Remarks
7-56
Defines a common area which is not erased by
the CHAINed program, and allows you to pass
variables from one program to another.
COMMON variable [,variable]...
is the name of a numeric or string variable which is required
to be passed to the CHAINed program. For array variables
place a set of parentheses "( )" after the variable name.
The COMMON statement is used in
conjunction with the CHAIN statement.
COMMON statements may appear anywhere
in a program, though it is recommended that
they appear at the beginning.
The CHAINed program need not specify,
through the use of COMMON statements, the
common variables specified by the CHAINing
program. The CHAINed program will use
those varia1Jles with the same names specified
in the CHAINing program. Each type
definition statement (DEFINT, DEFSNG,
DEFDBL, DEFSTR) referring to common
variables, must precede the associated
COMMON statements and must be repeated
in the CHAINed program.