xml attribute in double quotes

Where are you seeing "DTL response = <ID scope='Message'>3</ID>"?

What you see is the "representation", the "export" of your XML enabled class rendered by...whatever you are using to view/display it, the quotes are not part of the content.

How are you using/consuming your target (DTL response)? Some XML (SOAP? REST?) message? If so, I believe that you won't find single quotes when you will use it.

This is just guessing, because you don't provide any context/detail.

I think projecting as an attribute is enough. Here's an example:

Class Utils.Message Extends (%RegisteredObject, %XML.Adaptor)
{

Parameter XMLNAME = "ID";Property scope As%String(XMLPROJECTION = "ATTRIBUTE");

}

DTL:

Class Utils.DTL Extends Ens.DataTransformDTL
{

XData DTL [ XMLNamespace = "http://www.intersystems.com/dtl" ]
{
<transform sourceClass='Ens.Request' targetClass='Utils.Message' create='new' language='objectscript' >
<assign value='"Message"' property='target.scope' action='set' />
</transform>
}

/// do ##class(Utils.DTL).Test()ClassMethod Test()
{
	set source = ##class(Ens.Request).%New()
	#dim target As Utils.Message
	set sc = ..Transform(source, .target)
	do target.XMLExportToString(.xml)
	w xml, !
}

}

Results in:

>do##class(Utils.DTL).Test()

<ID scope="Message"></ID>