Table 20
+=============-===============================================================+
| Operation | Description |
| code type | |
|-------------+---------------------------------------------------------------|
| M | Mandatory - Commands so designated shall be implemented in |
| | order to meet the minimum requirement of this International |
| | Standard. |
| | |
| O | Optional - Commands so designated, if implemented, shall be |
| | implemented as defined in this International Standard. |
| | |
| V | Vendor-specific - Operation codes so designated are available|
| | for vendor defined commands. See the vendor specifications |
| | where compatibility is desired. |
| | |
| R | Reserved - Operation codes so designated shall not be used. |
| | They are reserved for future extensions to this |
| | International Standard. |
+=============================================================================+