Include comments in exported XML file

Question

When exporting an XMLObject (using Export/ExportString), is there any way to include a <!-- --> comment somewhere near the beginning of the file?

Note that it is not valid to put the comment as the very first line.

Answer 1

We can use the construction XMLObject["Comment"]["..."]. This is described in detail in this tutorial. For example...

ExportString[
  XMLElement["root", {}
  , { "\n"
    , XMLObject["Comment"][" hello "]
    , XMLElement["content", {}, {"content goes here"}]
    , "\n"
    }
  ]
, "XML"
]

... will generate this XML:

<root>
<!-- hello -->
<content>content goes here</content>
</root>

The documentation for XMLObject states that we can use this pattern to create various XML node types: declarations, comments, documents, doctypes, processing instructions and CDATA sections. Here is an example that shows each type:

ExportString[
  XMLObject["Document"][
    { XMLObject["Declaration"]["Version"->"1.0","Encoding"->"UTF-8","Standalone"->"no"]
    , XMLObject["Doctype"]["zot", "Public"->"-//???//zot", "System"->"urn://zot.zot"]
    }
  , XMLElement["zot", {}
    , { "\n"
      , XMLObject["Comment"][" witty remark "]
      , XMLElement["content", {}, {"to be determined"}]
      , "\n"
      , XMLObject["CDATASection"]["&&&!<><>!"]
      , "\n"
      , XMLObject["ProcessingInstruction"]["disposition: discard"]
      }
    ]
  , {}
  ]
, "XML"
]

yielding:

<?xml version='1.0' encoding='UTF-8' standalone='no'?>
<!DOCTYPE zot PUBLIC '-//???//zot' 'urn://zot.zot'>
<zot>
<!-- witty remark -->
<content>to be determined</content>
<![CDATA[&&&!<><>!]]>
<?disposition: discard?>
</zot>