SymDocumentWriter GetDocument(Document document)
{
if (document == null)
return null;
SymDocumentWriter doc_writer;
if (documents.TryGetValue (document.Url, out doc_writer))
return doc_writer;
doc_writer = writer.DefineDocument (
document.Url,
document.Language.ToGuid (),
document.LanguageVendor.ToGuid (),
document.Type.ToGuid ());
documents [document.Url] = doc_writer;
return doc_writer;
}