XDocumentType.SystemId Property

public:
 property System::String ^ SystemId { System::String ^ get(); void set(System::String ^ value); };

public string SystemId { get; set; }

public string? SystemId { get; set; }

member this.SystemId : string with get, set

Public Property SystemId As String

A String that contains the system identifier for this Document Type Definition (DTD).

The following example creates an XML document that refers to an external private DTD. The DTD does not have an internal subset. The call to the XDocumentType constructor reflects the use of the external private DTD. It passes null for the internal subset.

string pubsDtd =
@"<!ELEMENT Pubs (Book+)>
<!ELEMENT Book (Title, Author)>
<!ELEMENT Title (#PCDATA)>
<!ELEMENT Author (#PCDATA)>";
File.WriteAllText("Pubs.dtd", pubsDtd);

string target = "xml-stylesheet";
string data = "href=\"mystyle.css\" title=\"Compact\" type=\"text/css\"";

XDocument doc = new XDocument(
    new XDocumentType("Pubs", null, "Pubs.dtd", null),
    new XElement("Pubs",
        new XElement("Book",
            new XElement("Title", "Artifacts of Roman Civilization"),
            new XElement("Author", "Moreno, Jordao")
        ),
        new XElement("Book",
            new XElement("Title", "Midieval Tools and Implements"),
            new XElement("Author", "Gazit, Inbar")
        )
    ),
    new XComment("This is another comment.")
);
doc.Declaration = new XDeclaration("1.0", "utf-8", "true");
doc.Save("Pubs.xml");

// Validate Pubs.xml against Pubs.dtd.
XmlReaderSettings xrs = new XmlReaderSettings();
xrs.ProhibitDtd = false;
xrs.ValidationType = ValidationType.DTD;
xrs.ConformanceLevel = ConformanceLevel.Auto;
XmlReader xr = XmlReader.Create("Pubs.xml", xrs);
XDocument doc2 = XDocument.Load(xr);

XDocumentType dt = doc2.Document.DocumentType;
Console.WriteLine("SystemId:{0}", dt.SystemId);

Dim pubsDtd As String = _
    "<!ELEMENT Pubs (Book+)>" & Environment.NewLine & _
    "<!ELEMENT Book (Title, Author)>" & Environment.NewLine & _
    "<!ELEMENT Title (#PCDATA)>" & Environment.NewLine & _
    "<!ELEMENT Author (#PCDATA)>"
File.WriteAllText("Pubs.dtd", pubsDtd)

Dim target As String = "xml-stylesheet"
Dim data As String = "href='mystyle.css' title='Compact' type='text/css'"

Dim doc As XDocument = _
    <?xml version='1.0'?>
    <Pubs>
        <Book>
            <Title>Artifacts of Roman Civilization</Title>
            <Author>Moreno, Jordao</Author>
        </Book>
        <Book>
            <Title>Midieval Tools and Implements</Title>
            <Author>Gazit, Inbar</Author>
        </Book>
    </Pubs>
    <!--This is another comment.-->

doc _
.FirstNode _
.AddBeforeSelf(New XDocumentType("Pubs", Nothing, "Pubs.dtd", Nothing))

doc.Declaration = New XDeclaration("1.0", "utf-8", "true")
doc.Save("Pubs.xml")

' Validate Pubs.xml against Pubs.dtd.
Dim xrs As XmlReaderSettings = New XmlReaderSettings()
xrs.ProhibitDtd = False
xrs.ValidationType = ValidationType.DTD
xrs.ConformanceLevel = ConformanceLevel.Auto
Dim xr As XmlReader = XmlReader.Create("Pubs.xml", xrs)
Dim doc2 As XDocument = XDocument.Load(xr)

Dim dt As XDocumentType = doc2.Document.DocumentType
Console.WriteLine("SystemId:{0}", dt.SystemId)

This example produces the following output:

SystemId:Pubs.dtd

If an XML document uses an external private DTD, this property will contain the private identifier of the external DTD.

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