Throw the given error. When an error is thrown, the XQuery program execution is stopped.

let $x := xdmp:random(100)
return
if ( $x gt 50 ) 
then ( fn:error("ERROR", "greater than 50") )
else ( "Less than or equal to 50" )

=> The error when the random number is greater
   than 50.

Return the input $value unchanged and, if $label is the name of an enabled server event, emit that server event to the server log file (ErrorLog.txt) with $value as its data.

In order for the trace event to print out in the log file, you must enable the trace event in the Diagnostics page (Groups > group_name > Diagnostics ) of the Admin interface for the specified label.

fn:trace("This is a trace event.", "MY TRACE EVENT")

=> If MY TRACE EVENT is defined as an enabled trace event
   in the Diagnostics page of the Admin interface, then a
   message similar to the following is added to the 
   ErrorLog.txt file:

   2006-03-20 17:56:09.346 Info: [Event:id=MY TRACE EVENT] 
                                 This is a trace event.