Singular expression refers to non-unique object
This error message arises when you try to query a singular property of multiple objects. Relevance expressions require a match between the number of items in the argument and the plurality of the Inspector. For instance:
Q: character of "abc"
A: a
E: Singular expression refers to non-unique object.
This expression returns a single character, as requested by the singular Inspector character. However, the extra characters in the argument then generate the error. To avoid this error, use a plural expression:
Q: characters of "abc"
A: a
A: b
A: c
Every Inspector has both a singular and plural version. They are both listed for each Inspector in the appropriate guides.
To return a single value, you must query a single object.