Hi Sandra,
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"A mesh path expression is a special type of table expression and can be used in the same way as a table expression"
Refer: ABAP Keyword Documentation.
This statement explains the behaviour. I wrote a forward association to test this out and it is aligns with what you have mentioned.
out->next_section( 'Forward assoc: node2\to_node3' )->write( VALUE t_itab3( FOR <node3> IN mesh-node2\to_node3[ mesh-node2[ col1 = idx ] ] ( <node3> ) ) ).
mesh-node2[ col1 = idx ] returns a row of node2, which is then used to analyse the follow-on node3.
Thanks for clarifying.
BR,
Suhas