How to select following siblings until a certain sibling - xpath

Question

I'm currently working with VDA message types that have been convert to xml using a custom xml converter. However each header and line record in the source document is at the same level, as in the sample below:
<root>
<row>
<Record_type>512</Record_type>
<Customer_item_Number>A0528406</Customer_item_Number>
<Supplier_item_number>10962915</Supplier_item_number>
</row>
<row>
<Record_type>513</Record_type>
<Date>170306</Date>
<Quantity>115</Quantity>
</row>
<row>
<Record_type>513</Record_type>
<Date>190306</Date>
<Quantity>97</Quantity>
</row>
<row>
<Record_type>512</Record_type>
<Customer_item_Number>A0528433</Customer_item_Number>
<Supplier_item_number>10962916</Supplier_item_number>
</row>
<row>
<Record_type>513</Record_type>
<Date>170306</Date>
<Quantity>115</Quantity>
</row>
<row>
<Record_type>513</Record_type>
<Date>170306</Date>
<Quantity>115</Quantity>
</row>
<row>
<Record_type>513</Record_type>
<Date>170306</Date>
<Quantity>115</Quantity>
</row>
<row>
<Record_type>513</Record_type>
<Date>170306</Date>
<Quantity>115</Quantity>
</row>
</root>
(512) record types are headers, the following (513) record types are lines for the preceding (512) record above it.
I am struggling to format this message, so that the lines (513) are indented underneath each header (512) record.
i.e. required output, something like this.
<root>
<Header>
<Record_type>512</Record_type>
<Customer_item_Number>A0528406</Customer_item_Number>
<Supplier_item_number>10962915</Supplier_item_number>
<Line>
<Record_type>513</Record_type>
<Date>170306</Date>
<Quantity>115</Quantity>
</Line>
<Line>
<Record_type>513</Record_type>
<Date>190306</Date>
<Quantity>97</Quantity>
</Line>
</Header>
<Header>
<Record_type>512</Record_type>
<Customer_item_Number>A0528433</Customer_item_Number>
<Supplier_item_number>10962916</Supplier_item_number>
<Line>
<Record_type>513</Record_type>
<Date>170306</Date>
<Quantity>115</Quantity>
</Line>
<Line>
<Record_type>513</Record_type>
<Date>170306</Date>
<Quantity>115</Quantity>
</Line>
<Line>
<Record_type>513</Record_type>
<Date>170306</Date>
<Quantity>115</Quantity>
</Line>
<Line>
<Record_type>513</Record_type>
<Date>170306</Date>
<Quantity>115</Quantity>
</Line>
</Header>
</root>
I have had some success using following sibling, but I'm unable to link this with preceding-sibling, to filter out only the required records before the next loop.
I am hoping someone will be able to assist. :)

Answer 1

In XQuery 3.1 you can use a tumbling window https://www.w3.org/TR/xquery-31/#id-tumbling-windows:
<root>
{
for tumbling window $record in root/row
start $s when $s/Record_type = 512
return
<Header>
{
head($record)/*,
tail($record) !
<Line>
{ * }
</Line>
}
</Header>
}
</root>
https://xqueryfiddle.liberty-development.net/gWcDMef

Answer 2

If your XQuery processor supports XQuery 3.0's window clauses, your query is (at least conceptually) very straight forward and efficient:
<root>{
for tumbling window $w in /root/row
start when true()
end next $n when $n/Record_type = '512'
return <Header>{
head($w)/*,
for $line in tail($w)
return <Line>{$line/*}</Line>
}</Header>
}</root>
Otherwise you have to use the preceding-sibling and following-sibling XPath axes as Mads Hansen also shows in his answer:
<root>{
for $header in /root/row[Record_type = '512']
return <Header>{
$header/*,
for $line in $header/following-sibling::row[Record_type = '513']
let $prev-headers := $line/preceding-sibling::row[Record_type = '512']
where $prev-headers[last()] is $header
return <Line>{$line/*}</Line>
}</Header>
}</root>
Here we get all lines after the current header first, and then check for each line if the last header before it is the current one. It is important here to use is instead of = or eq because the latter two work on atomic items only. This means that XML nodes are atomized (i.e., stripped down to just their concatenated text contents) before the comparison is performed. The is operator compares node identity instead.

Answer 3

For every row that has a Record_type of 512, create a Header element.
In order to find the row elements for the relevant group of Line elements, you want to select the row elements that are following-sibling from the 512 who's Record_type = 513 and who's first preceding-sibling is the current header.
for $header in $doc/root/row[Record_type = 512]
let $lines := $header/following-sibling::row[Record_type = 513]
[preceding-sibling::row[Record_type = 512][1] = $header]
return
<Header>{
$header/*,
for $line in $lines
return <Line>{ $line/* }</Line>
}</Header>