I’m using some of the YUI CSS files to make sure fonts look the same when viewed in IE and Firefox. For the Yahoo stuff to work correctly, you need a doctype of HTML 4.01 Strict so that the browser doesn’t go into quirks mode.

The HTML I’m creating is generated from a XSL transform using C# under the .NET Framework 2.0. I based my transform code off an example from MSDN and figured the XSLT file would handle the formatting options from within the xsl:output tag.

<xsl:output method='html' indent='yes' doctype-public='-//W3C//DTD HTML 4.01//EN' doctype-system='http://www.w3.org/TR/html4/strict.dtd' />

I had this problem where every time I ran the XSL transform, the resulting HTML document would have no doctype at all. The problem is that I was passing a XmlWriter to the XslCompiledTransform.Transform method, as is shown in most examples. It makes sense now that I think about it, though: strict HTML isn’t well-formed XML. I tried using XmlOutputMethod to force it into HTML, but, of course, this setting is obtained from the XSL declaration above.

If you’re not outputting an XML document, use a StreamWriter to write the transformed file.

XPathDocument xp = new XPathDocument(xml);
XslCompiledTransform xslt = new XslCompiledTransform();
StreamWriter sw = new StreamWriter(outfile);
xslt.Load(xsl);
xslt.Transform(xp, null, sw);
sw.Close();

For XHTML, I imagine the XmlWriter would work fine.