itmlst
    OpenVMS usage:item_list_3
    type:         longword (unsigned)
    access:       read only
    mechanism:    by reference
    The itmlst argument is the address of a list of item descriptors,
    each of which describes an item of information. The list of item
    descriptors is terminated by a longword of 0.
    The service takes one argument as input, an item list. This item
    list has the following format for a single item descriptor:
    63                31                  0
    +-------------------------------------+
    |  Buffer length   |    Item code     | STENVDEF$L_ITEM_CODE/STENVDEF$L_BUF_LEN
    +-------------------------------------+
    |           Buffer address            | STENVDEF$Q_BUF_ADDR
    +-------------------------------------+
    |       Return length address         | STENVDEF$Q_RET_ADDR
    +-------------------------------------+
    The following table defines the item descriptor fields:
    Descriptor
    Field          Definition
    Item code      A longword indicating which environment variable
                   you want to retrieve. These codes are defined in
                   $STENVDEF.
    Buffer         A longword specifying the length of the buffer
    length         in which GETENV is to write the environment
                   variable's value.
    Buffer         A quadword indicating the address of the buffer
    address        in which GETENV is to write the environment
                   variable's value.
    Return         A quadword indicating the return address in
    length         which to put the length of the value that GETENV
    address        retrieved.