Error message for nodeset returned when single node expected is generally unhelpful

[lognaturel]

When a nodeset is returned but a single node is expected, the error message says "This field is repeated:" and "You may need to use the indexed-repeat() function to specify which value you want".

The most common case I see this error in is when a choice filter returns multiple items. Another common case is trying to access a field in a repeat from outside the repeat. The intent is often to use some kind of aggregating function like sum.

The indexed-repeat hint is not useful in either of those cases. It only really applies to parallel repeats. Even then, we try to nudge form creators towards using raw XPath expressions over indexed-repeat.