The text and Note say (partially):

<quote>
Writing the expression as for $v in S return R, the two operand roles are S and R.

<snip />

<note>
The rule that R must be grounded prevents the variable being bound to a node in a streamed document. This disallows expressions of the form for $x in child::section return $x/para, because this requires data flow analysis (tracing from the binding of a variable to its usages), rather than purely syntactic analysis. Some implementations may be able to stream such constructs.
</note>
</quote>

But this is not (entirely) true. It is "S" that must be grounded that prevents the variable from being bound to a node.

The rest of the text seems correct.

Note that we could make "for $n in para return copy-of($n/@indent)" streamable, because the operand R is motionless, but currently we disallow this.