Alex,
I did download your sample which was brilliant but unfortunately does not seem to work in my case.
Because My Repeating Group (Table) is linked to an XML CAML data connection, the Default Value Function (Fx) button under the Data Tab is greyed out, not allowing me to add a formula such as substring-before(substring-after(concat(index = count(preceding-sibling::*[local-name() = "Field(XML_CAML_Read)"]), ThisPONumber, "true", ., "true"), "true"), "true")
Any other ideas, BTW you have a Typo "ue" instead of "True" in the example formula: substring-before(substring-after(concat(index = count(preceding-sibling::*[local-name() = "RepeatingGroup"]), NewValue, "true", ., "true"), "ue"), "true") - but it still works.
Thanks,
Brian