Linq to Xml and custom xml entities

Question

I want to create a MathML document from an expression tree using Linq to xml, but I cannot figure out how to use the MathML xml entities (such as ⁡ and &InvisibleTimes): When I try to create directly a XElement using

XElement xe = new XElement("mo", "&InvisibleTimes");

it justs escapes the ampersand (which is no good). I also tried to use XElement.Parse

XElement xe = new XElement.Parse("<mo>&InvisibleTimes</mo>");

but it fails with an System.XmlException: Reference to undeclared entity 'InvisibleTimes' How can I declare the entity or ignore the checks?

Answer 1

As others have pointed out, there is no direct way to do it.

That said, you can try using the corresponding unicode caracther. According to http://www.w3.org/TR/MathML2/mmlalias.html, for ApplyFunction it is 02061, try new XElement("mo", "\u02061")

Answer 2

According to this thread, LINQ to XML doesn't include entity references: it doesn't have any node type for them. It just expands them as it loads a file, and after that you've just got "normal" characters.

Answer 3

I don't know about XDocument, but you can do it with XmlDocument:

XmlDocument doc = new XmlDocument();
var entity = doc.CreateEntityReference("InvisibleTimes");
XmlElement root = (XmlElement)doc.AppendChild(doc.CreateElement("xml"));
var el = root.AppendChild(doc.CreateElement("mo")).AppendChild(entity);
string s = doc.OuterXml;

Answer 4

You may need to xml encode the names because '&' is a special character.

So instead of

XElement xe = new XElement("mo", "&InvisibleTimes");

try

XElement xe = new XElement("mo", "&InvisibleTimes");

Answer 5

I think you'll need a DTD to define <mo>&InvisibleTimes;</mo>.

MathML 2.0 provides an XHTML + MathML DTD.

Answer 6

A workaround is to use any placeholder for the & such as ;_amp_; XElement xe = new XElement("mo", ";_amp_;InvisibleTimes) and restore it when you get the xml string: output = xe.ToString().Replace(";_amp_;", "&")