How to replace the $content value in transformation?

I need to replace the $content value in my transformation.

xquery version "1.0-ml";

module namespace test =
  "http://marklogic.com/rest-api/transform/security-load";

declare function test:transform(
    $context as map:map,
    $params as map:map,
    $content as document-node()
) as document-node()
{       
        let $jsonObj := xdmp:from-json($content)
        let $inputval := "fname,lname"
        let $entity :="holidayDate"
        let $domain :="referenceData"


        let $uri := xdmp:apply(
            xdmp:function(xs:QName("createUri"), "/wdsUtils.sjs"),
            $jsonObj,
            $inputval)


        let $root := xdmp:apply(
            xdmp:function(xs:QName("addMetaData"), "/wdsUtils.sjs"),
            $entity,
            $domain,
            $jsonObj)

        let $output := $root    

        return map:put($context,"uri",$uri),
        document { $output }
};

I need to change the $content value with $root value and return it. I was trying to return $root directly but it didn't work, I was getting invalid document error.

The problem is that $output is scoped to the FLWOR statement, but you're referring to it outside of that statement. See the parentheses in the return below.

xquery version "1.0-ml";

module namespace test = "http://marklogic.com/rest-api/transform/security-load";

declare function test:transform(
    $context as map:map,
    $params as map:map,
    $content as document-node()
) as document-node()
{       
    let $jsonObj := xdmp:from-json($content)
    let $inputval := "fname,lname"
    let $entity :="holidayDate"
    let $domain :="referenceData"

    let $uri := 
        xdmp:apply(
            xdmp:function(xs:QName("createUri"), "/wdsUtils.sjs"),
            $jsonObj,
            $inputval
        )

    let $root := 
        xdmp:apply(
            xdmp:function(xs:QName("addMetaData"), "/wdsUtils.sjs"),
            $entity,
            $domain,
            $jsonObj
        )

    let $output := $root    

    return (
        map:put($context,"uri",$uri),
        document { $output }
    )
};