When connecting to a server using the DRDA protocol, is it true that the first Client-To-Server command MUST be EXCSAT chained with ACCSEC?

Question

When connecting to a server using the DRDA protocol, is it true that the first Client-To-Server command MUST be EXCSAT chained with ACCSEC?

I found 2 different answers when I googled it.

If you look at The Open Group web site (https://collaboration.opengroup.org/dbiop/) it can be understood that the answer is NO.

However, if you look at the IBM website (http://publib.boulder.ibm.com/infocenter/dzichelp/v2r2/index.jsp?topic=%2Fcom.ibm.ims11.doc.apr%2Fims_ddm_excsat.htm) you can understand the answer is YES.

So which is it?