PS specifies that programmed symbols are to be used.
This overrides any PS operand set by the DFHMDI macro or the DFHMSD macro.
BASE is the default and specifies that the base symbol set is to be used.
psid specifies a single EBCDIC character, or a hexadecimal code of the form X'nn', that identifies the set of programmed symbols to be used.
The PS operand is ignored unless the terminal supports programmed symbols, as indicated by PROGSYMBOLS(YES) on the RDO TYPETERM definition.
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https://www.ibm.com/support/knowledgecenter/en/SSGMCP_5.3.0/com.ibm.cics.ts.applicationprogramming.doc/topics/dfhp473.html