[F&O] IBM-FO-011: Trace function

(IBM-FO-011) Section 4, The Trace Function: I suggest that the actual 
creation of a trace data set be made optional. Say that this function 
supports debugging of queries in a portable way, by allowing an 
implementation to optionally provide a data set containing a trace of 
execution. The only normative requirement for this function is that it 
returns its first argument. If an implementation chooses to provide a 
trace data set, the string values of the first and second arguments are 
directed to the trace data set. (Location, format, and ordering are 
implementation-dependent, as stated.) In effect, fn:trace becomes a 
function that systems can either implement or ignore without raising an 
error. 

--Don Chamberlin