It is a static error (err:XS0037) if ... any element in the XProc namespace other than p:inline directly contains text nodes that do not consist entirely of whitespace.
applies equally here. My processor detects err:XS0037 long before it considers that this is text in an input binding.
I think
err:XS0037:applies equally here. My processor detects
err:XS0037long before it considers that this is text in an input binding.