```
In [1]: from lxml import etree

```

I've got an HTML document:

```
In [2]: root = etree.fromstring(u'''<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN">\n<HTML></HTML>''', etree.HTMLParser())

```

Its doctype is parsed correctly:

```
In [3]: root.getroottree().docinfo.doctype
Out[3]: u'<!DOCTYPE html PUBLIC "-//IETF//DTD HTML//EN">'

```

But when serializing it, I am losing it:

```
In [4]: etree.tostring(root.getroottree(), method='html')
Out[4]: '<html></html>'

```

What should I do to get that doctype serialized?

Debian GNU/Linux, Sid. Python 2.6.6. lxml 2.2.8-2.