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<result>
    <original>
        <ref xmlns="http://www.tei-c.org/ns/1.0" xmlns:frus="http://history.state.gov/frus/ns/1.0">
            <hi rend="italic">Foreign Relations,</hi> 1952–1954, vol. VII, Part 2 </ref>, p.
        1914.</original>
    <analysis>
        <fn:analyze-string-result xmlns:fn="http://www.w3.org/2005/xpath-functions">
            <fn:match>
                <fn:group nr="1">, p. </fn:group>
                <fn:group nr="2">1914</fn:group>
                <fn:group nr="3">.</fn:group>
            </fn:match>
        </fn:analyze-string-result>
    </analysis>
    <new>
        <ref xmlns="http://www.tei-c.org/ns/1.0">
            <hi xmlns:frus="http://history.state.gov/frus/ns/1.0" rend="italic">Foreign
                Relations,</hi> 1952–1954, vol. VII, Part 2 , p. 1914</ref>.</new>
</result>

<note xmlns="http://www.tei-c.org/ns/1.0" xmlns:frus="http://history.state.gov/frus/ns/1.0"> For
    text of NSC 164/1, see <ref>
        <hi rend="italic">Foreign Relations,</hi> 1952–1954, vol. VII, Part 2 </ref>, p.
    1914.</note>

xquery version "3.0";

(:
Same as https://gist.github.com/joewiz/2369367de3babba30e0aad8c9beec893, except I've removed local:reconstruct().
Note that unwanted namespace declarations appear inline in the result - see 03-test-results.xml line 17.
:)

declare namespace tei="http://www.tei-c.org/ns/1.0";

let $doc := doc('02-sample.xml')
let $refs := $doc//tei:ref
    [matches(following-sibling::node()[1][. instance of text()], '^, pp?\.\s+\d+')]
for $ref in $refs
let $following-text := $ref/following-sibling::text()[1]
let $analyze := analyze-string($following-text, '^(, pp?\.\s+)(\d+)(.*)$')
let $new-ref := 
    (
    element 
        { QName('http://www.tei-c.org/ns/1.0', 'ref') }
        { 
            $ref/node(),
            string-join($analyze/fn:match/fn:group[@nr = (1, 2)])
        }
    )
let $new-following-text := string-join($analyze/fn:match/fn:group[@nr ge 3])
let $test := 
    <result>
        <original>{$ref, $following-text}</original>
        <analysis>{$analyze}</analysis>
        <new>{$new-ref, $new-following-text}</new>
    </result>
return 
    
    (:
    $test
    :)
    
    (
    replace node $ref with $new-ref
    ,
    replace node $following-text with $new-following-text
    )