Is `external store` support with Oracle TDE in the version 12.1.0.2?

Hi,

When I read the documentation of Oracle 12.1.0.2, I see that the  'EXTERNAL STORE' are supported .

https://docs.oracle.com/database/121/ASOAG/managing-keystore-and-tde-master-encryption-key.htm#GUID-E72639A8-43B7-4EAC-B0F9-85DF4A714E3A

But I see that the SQL reference document does not mention about the 'EXTERNAL STORE'

https://docs.oracle.com/database/121/SQLRF/statements_1003.htm#BGEJBIFJ

Also I am unable to set the EXTERNAL STORE CREDENTIAL LOCATION. Please refer to console output below for Oracle 12.1.0.2.

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SQL> alter system set EXTERNAL_KEYSTORE_CREDENTIAL_LOCATION='/tmp/oracle' scope=spfile;

alter system set EXTERNAL_KEYSTORE_CREDENTIAL_LOCATION='/tmp/oracle' scope=spfile