symbol-name

    Specifies a string of 1 to 255 characters for the symbol name.
    The name can contain any alphanumeric characters from the DEC
    Multinational character set, the underscore (_),  and the dollar
    sign ($).  However, the name must begin only with an alphabetic
    character (uppercase and lowercase characters are equivalent),
    an underscore, or a dollar sign. Using one equal sign (=)  places
    the symbol name in the local symbol table for the current command
    level. Using two equal signs (==) places the symbol name in the
    global symbol table.

 expression

    Names the value on the right-hand side of an assignment
    statement. This parameter can consist of a character string, an
    integer, a symbol name, a lexical function, or a combination of
    these entities. The components of the expression are evaluated,
    and the result is assigned to the symbol. All literal character
    strings must be enclosed in quotation marks (" ").  If the
    expression contains a symbol, the expression is evaluated using
    the symbol's value.

    The result of expression evaluation is either a character string
    or a signed integer value. If the expression is evaluated as a
    string, the symbol is assigned a string value. If the expression
    is evaluated as an integer, the symbol is assigned an integer
    value. If the integer value exceeds the capacity of the 4-byte
    buffer that holds it, no error message is issued.

    For a summary of operators used in expressions, details on
    how to specify expressions, and details on how expressions are
    evaluated, see the OpenVMS User's Manual.

    DCL uses a buffer that is 1024 bytes long to hold an assignment
    statement and to evaluate the expression. The length of the
    symbol name, the expression, and the expression's calculations
    cannot exceed 1024 bytes.

 [bit-position,size]

    States that a binary overlay is to be inserted in the current
    32-bit value of a symbol name. The current value of the symbol
    name is evaluated. Then, the specified number of bits is replaced
    by the result of the replacement expression. The bit position is
    the location relative to bit 0 at which the overlay is to occur.
    If the symbol you are overlaying is an integer, then the bit
    position must be less than 32. The sum of the bit position and
    the size must be less than or equal to 32.

    If the symbol you are overlaying is a string, then the bit
    position must be less than 6152. Because each character is
    represented using 8 bits, you can begin an overlay at any
    character through the 768th character. (The 768th character
    starts in bit position 6144.) The sum of the bit position and
    the size must be less than or equal to 6152.

    The size is the number of bits to be overlaid. If you specify a
    size that is greater than 32, DCL reduces the size to 32.

    The brackets are required notation; no spaces are allowed between
    the symbol name and the left bracket. Specify values for the bit
    position and size as integers.

 replacement-expression

    Specifies the value that is used to overlay the symbol you are
    modifying. Specify the replacement expression as an integer.

    If the symbol you are modifying is an integer, the replacement
    expression defines a bit pattern that is overlaid on the value
    assigned to the symbol. If the symbol you are modifying is
    a character string, the result of the replacement expression
    defines a bit pattern that is overlaid on the specified bits
    of the character string. If the symbol you are modifying is
    undefined, the result of the replacement expression is overlaid
    on a null string.