[sv-ec] only singular types allowed in mailboxes

There is no explicit statment that mailbox allows only singular types, but
mailbox functions headers are:
task put( singular message);

While singular is defined as:
    A singular type shall be any data type except an unpacked structure,
unpacked union, or unpacked array

From above I can tell that unpacked strucures is forbidden for mailboxes
(both parametrized and not parametrized) was it intented restriction?
Is there any rationale behind that?
 
 
DANiel

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