Odd sysdate construction

select SYSDATE@! from dual;
This appeared in a client query (actually it was trunc(sysdate@!) ) What is the @!? Its valid in the Oracle takes it but I can't find any = documentation as to what it is. It seems to act the same as plain old = sysdate. But it's the only place where @! Is allowed.

Don Freeman
Database Administrator 1
Pennsylvania Dept of Health
Bureau of Information Technology

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