These indentifiers must not be used when creating new messages.
The following only applies to processing messages that were
created using old software.
Since the "IBMPC" identifier, initially used to indicate IBM
codepage 437, eventually evolved into identifying "any IBM
codepage", there exists in some implementations an additional
control line, "CODEPAGE", identifying the messages codepage:
"^ACODEPAGE: xxx
This use is deprecated in favour of the "CPxxx" identifiers
defined above. If found in incoming messages, however, it should
be used as an override of the "CHRS: IBMPC" identifier.
Note the words "MUST NOT" in the first line of this paragraph. So when will you make your software FS-5003 complient?