Saxon

declare function local:join($done, $current, $todo)

{

if (empty($todo)) then

string-join(($done, $current), "
")

else

let $item := $todo[1]

let $todo := $todo[position() > 1]

return

typeswitch ($item)

case element(tab) return

local:join(($done, $current), (), $todo)

case processing-instruction() return

local:join($done, $current, (<tab/>, $todo))

default return

local:join($done, string-join(($current, $item)), $todo)

};

let $rendered := <root><tab col="1"/><fragment><name>json</name></fragment><tab col="9"/>::=<name>value</name><name>eof</name><tab col="1"/><fragment><name>object</name></fragment><tab col="9"/>::= '{{'(<name>pair</name>(','<name>pair</name><fragment>)*</fragment><fragment>)?</fragment>'}}'<tab col="1"/><fragment><name>pair</name></fragment><tab col="9"/>::=<name>string</name>':'<name>value</name><tab col="1"/><fragment><name>array</name></fragment><tab col="9"/>::= '['(<name>value</name>(','<name>value</name><fragment>)*</fragment><fragment>)?</fragment>']'<tab col="1"/><fragment><name>value</name></fragment><tab col="9"/>::=<name>string</name><tab col="11"/>|<name>number</name><tab col="11"/>|<name>object</name><tab col="11"/>|<name>array</name><tab col="11"/>| 'true'<tab col="11"/>| 'false'<tab col="11"/>| 'null'<tab col="1"/><fragment><name>ws</name></fragment><tab col="9"/>::=<name>whitespace^token</name><tab col="10"/>/* ws: definition */<?TOKENS?><tab col="1"/><fragment><name>eof</name></fragment><tab col="9"/>::= $<tab col="1"/><fragment><name>string</name></fragment><tab col="9"/>::= '"' (<name>anyUnicodeCharacterExceptQuoteOrBackslashOrControlCharacter</name>| '\"' | '\\' | '\/' | '\b' | '\f' | '\n' | '\r' | '\t' | '\u'<name>fourHexadecimalDigits</name><fragment>)*</fragment>'"'<tab col="1"/><fragment><name>anyUnicodeCharacterExceptQuoteOrBackslashOrControlCharacter</name></fragment><tab col="9"/>::=<name>alphabet</name>- ["#x005C]<tab col="1"/><fragment><name>alphabet</name></fragment><tab col="9"/>::= #x0009<tab col="11"/>| #x000A<tab col="11"/>| #x000D<tab col="11"/>| [#x0020-#xD7FF]<tab col="11"/>| [#xE000-#xFFFD]<tab col="11"/>| [#x10000-#x10FFFF]<tab col="1"/><fragment><name>hexadecimalDigit</name></fragment><tab col="9"/>::= [0-9A-Fa-f]<tab col="1"/><fragment><name>fourHexadecimalDigits</name></fragment><tab col="9"/>::=<name>hexadecimalDigit</name><name>hexadecimalDigit</name><name>hexadecimalDigit</name><name>hexadecimalDigit</name><tab col="1"/><fragment><name>number</name></fragment><tab col="9"/>::=<fragment>'-'?</fragment>( '0' |<name>digitOneThroughNine</name><fragment><name>digit</name>*</fragment>)('.'<fragment><name>digit</name>+</fragment><fragment>)?</fragment>(( 'e' | 'E' ) ( '+' | '-'<fragment>)?</fragment><fragment><name>digit</name>+</fragment><fragment>)?</fragment><tab col="1"/><fragment><name>digit</name></fragment><tab col="9"/>::= [0-9]<tab col="1"/><fragment><name>digitOneThroughNine</name></fragment><tab col="9"/>::=<name>digit</name>- '0'<tab col="1"/><fragment><name>whitespace</name></fragment><tab col="9"/>::=<fragment>[#x0009#x000A#x000D#x0020]+</fragment></root>

return local:join((), (), $rendered/node())