You can't serialize a free-floating attribute node

[ndw]

In the section on text value templates, we say that inserting XML into a non-XML document via a TVT inserts the serialization. But there's evidence in the wild of this usage:

<p:inline content-type="text/plain">{/*/@name}</p:inline>

with the expectation that the value of the name attribute is inserted. Either we need to special case inserting free-floating attributes or that's an error.

[ndw]

Having fixed a bug where I was doing TVTs in text/plain incorrectly, I have to say I'm unhappy with the results. Consider:

<p:with-input>
  <p:inline content-type="text/plain" expand-text="false"><![CDATA[
print("<?xml version='1.0'?>")
print(f"<doc>Testing {x*y}</doc>")
  ]]></p:inline>
</p:with-input>

Unless I've done something else wrong, absolutely a possibility, that produces:

print("<?xml version='1.0'?>")
print(f"<doc>Testing {x*y}</doc>")

Which is ... utterly useless.

[ndw]

Setting aside, for a moment, the annoying problem of backwards incompatibility, having the TVT output be special variation on cast-content-type seems wrong. Maybe serializing with the text method makes more sense.

[xml-project]

Maybe serializing with the text method makes more sense.

Yes, I think that makes much more sense. Seriously I can't hardly think about a use case for adding nodes with method "xml" here.
For the "free-floating attribute node" we could either say it's an error or invent a special case using their string values.

[gimsieke]

Can’t we tell people to write <p:inline content-type="text/plain">{string(/*/@name)}</p:inline>?

[ndw]

Document that it's technically incompatible, but can't possibly be useful. Editor to figure out what to do with the error code. Agree with Gerrit, use string().

[ndw]

I couldn't find a suitable error so I added err:XD0084.