This could do with some comments to explain what it's doing and why we're iterating over both sides.

Similarly flip this to true and set it false if you get something

Similarly flip this to true and set it false if you get something

Probably better to set aIsUndefined := true and then only set it to false at line 193

So if we get an NPE we fall down to line 37 where we guess a delimiter on an empty []byte and create a reader on the empty input?

I would worry that in this case the rd would be nil and we'd get an NPE below.

ioutil cannot return io.EOF

This may be wrong for other renderers. You could check in the csv renderer for `io.EOF` and treat it as no error.