Add Document struct

src/element.rs

@@ -99,3 +99,9 @@ impl Element {
         self
     }
 }
+
+/// An HTML document.
+///
+/// A `Document(el)` is basically the same as `[Content::doctype(), el.into()]`
+/// for the purposes of the [`crate::Render`] trait.
+pub struct Document(pub Element);

src/render.rs

@@ -3,6 +3,7 @@ use std::{error, fmt};
 use crate::{
     check,
     element::{Content, Element, ElementKind},
+    Document,
 };
 
 #[derive(Debug)]
@@ -81,6 +82,14 @@ pub trait Render {
     }
 }
 
+impl Render for Document {
+    fn render<W: fmt::Write>(&self, w: &mut W) -> Result<()> {
+        Content::doctype().render(w)?;
+        self.0.render(w)?;
+        Ok(())
+    }
+}
+
 impl Render for [Content] {
     fn render<W: fmt::Write>(&self, w: &mut W) -> Result<()> {
         for content in self {