...
listToString() can be used to format a list (of errors, say) into a string that can be recorded in a string-valued field on a stream record. Given a list like:
$errors = ["Bad input", "Missing rate value"],
the expression
listToString($errors, "\n") and listToString($errors, ", ")
will generate output strings like:
"Bad input
Missing rate value"
and
"Bad input, Missing rate value"
respectively.