diff --git a/README.md b/README.md
index bcfee63..3cfcb84 100644
--- a/README.md
+++ b/README.md
@@ -20,32 +20,38 @@ extern crate orgize;
 
 ## Example
 
+### Using Parser
+
+Orgize parser acts like a event-based parser, which means it returns an
+`Iterator` of `Event` s.
+
 ```rust
 use orgize::Parser;
 
-let parser = Parser::new(
-    r"* Title 1
+let parser = Parser::new(r#"* Title 1
 *Section 1*
 ** Title 2
 _Section 2_
 * Title 3
 /Section 3/
 * Title 4
-=Section 4=",
-);
+=Section 4="#);
 
 for event in parser {
     // handling the event
 }
 ```
 
-Alternatively, you can use the built-in render.
+### Using Render
+
+You can use the built-in `HtmlRender` to generate html string directly:
 
 ```rust
-use orgize::export::DefaultHtmlRender;
-use std::io::Cursor;
+use orgize::export::HtmlRender;
+use std::io::{Cursor, Result};
 
-let contents = r"* Title 1
+fn main() -> Result<()> {
+    let contents = r"* Title 1
 *Section 1*
 ** Title 2
 _Section 2_
@@ -54,14 +60,96 @@ _Section 2_
 * Title 4
 =Section 4=";
 
-let cursor = Cursor::new(Vec::new());
-let mut render = DefaultHtmlRender::new(cursor, &contents);
+    let mut cursor = Cursor::new(Vec::new());
+    let mut render = HtmlRender::default(&mut cursor, &contents);
 
-render
-    .render()
-    .expect("something went wrong rendering the file");
-    
-let result = String::from_utf8(render.into_writer().into_inner()).expect("invalid utf-8");
+    render.render()?;
+
+    assert_eq!(
+        String::from_utf8(cursor.into_inner()).unwrap(),
+        "<h1>Title 1</h1><section><p><b>Section 1</b></p></section>\
+         <h2>Title 2</h2><section><p><u>Section 2</u></p></section>\
+         <h1>Title 3</h1><section><p><i>Section 3</i></p></section>\
+         <h1>Title 4</h1><section><p><code>Section 4</code></p></section>"
+    );
+
+    Ok(())
+}
+```
+
+### Custom HtmlHandler
+
+You can create your own handler by implementing `HtmlHandler` trait and passing
+it to the `HtmlRender`.
+
+The following example demonstrates how to add an anchor for every headline and
+use your own error type.
+
+```rust
+use orgize::{export::*, headline::Headline};
+use slugify::slugify;
+use std::io::{Cursor, Error as IOError, Write};
+use std::string::FromUtf8Error;
+
+// custom error type
+#[derive(Debug)]
+enum Error {
+    IO(IOError),
+    Headline,
+    Utf8(FromUtf8Error),
+}
+
+// From<std::io::Error> trait is required for custom error type
+impl From<IOError> for Error {
+    fn from(err: IOError) -> Error {
+        Error::IO(err)
+    }
+}
+
+struct CustomHtmlHandler;
+
+impl<W: Write> HtmlHandler<W, Error> for CustomHtmlHandler {
+    fn headline_beg(&mut self, w: &mut W, hdl: Headline) -> Result<(), Error> {
+         if hdl.level > 6 {
+             Err(Error::Headline)
+         } else {
+             write!(
+                 w,
+                 r##"<h{}><a class="anchor" href="#{}">"##,
+                 hdl.level,
+                 slugify!(hdl.title),
+             )?;
+             self.escape(w, hdl.title)?;
+             Ok(write!(w, "</a></h{}>", hdl.level)?)
+         }
+    }
+}
+
+fn main() -> Result<(), Error> {
+    let contents = r"* Title 1
+*Section 1*
+** Title 2
+_Section 2_
+* Title 3
+/Section 3/
+* Title 4
+=Section 4=";
+
+    let mut cursor = Cursor::new(Vec::new());
+    let mut render = HtmlRender::new(CustomHtmlHandler, &mut cursor, &contents);
+
+    render.render()?;
+
+    assert_eq!(
+        String::from_utf8(cursor.into_inner()).map_err(Error::Utf8)?,
+        "<h1><a class=\"anchor\" href=\"#title-1\">Title 1</a></h1><section><p><b>Section 1</b></p></section>\
+         <h2><a class=\"anchor\" href=\"#title-2\">Title 2</a></h2><section><p><u>Section 2</u></p></section>\
+         <h1><a class=\"anchor\" href=\"#title-3\">Title 3</a></h1><section><p><i>Section 3</i></p></section>\
+         <h1><a class=\"anchor\" href=\"#title-4\">Title 4</a></h1><section><p><code>Section 4</code></p></section>"
+    );
+
+    Ok(())
+}
 ```
 
 ## License
diff --git a/src/lib.rs b/src/lib.rs
index efb0b59..50d1df7 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,33 +1,41 @@
 //! A Rust library for parsing orgmode files.
 //!
-//! ## Example
+//! # Using Parser
+//!
+//! Orgize parser acts like a event-based parser, which means it
+//! returns an `Iterator` of [`Event`] s.
+//!
+//! [`Event`]: enum.Event.html
 //!
 //! ```rust
 //! use orgize::Parser;
 //!
-//! let parser = Parser::new(
-//!     r"* Title 1
+//! let parser = Parser::new(r#"* Title 1
 //! *Section 1*
 //! ** Title 2
 //! _Section 2_
 //! * Title 3
 //! /Section 3/
 //! * Title 4
-//! =Section 4=",
-//!     );
+//! =Section 4="#);
 //!
 //! for event in parser {
 //!     // handling the event
 //! }
 //! ```
 //!
-//! Alternatively, you can use the built-in render directly:
+//! # Using Render
+//!
+//! You can use the built-in [`HtmlRender`] to generate html string directly:
+//!
+//! [`HtmlRender`]: export/struct.HtmlRender.html
 //!
 //! ```rust
 //! use orgize::export::HtmlRender;
-//! use std::io::Cursor;
+//! use std::io::{Cursor, Result};
 //!
-//! let contents = r"* Title 1
+//! fn main() -> Result<()> {
+//!     let contents = r"* Title 1
 //! *Section 1*
 //! ** Title 2
 //! _Section 2_
@@ -36,41 +44,76 @@
 //! * Title 4
 //! =Section 4=";
 //!
-//! let mut cursor = Cursor::new(Vec::new());
-//! let mut render = HtmlRender::default(&mut cursor, &contents);
+//!     let mut cursor = Cursor::new(Vec::new());
+//!     let mut render = HtmlRender::default(&mut cursor, &contents);
 //!
-//! render
-//!     .render()
-//!     .expect("something went wrong rendering the file");
+//!     render.render()?;
 //!
-//! let result = String::from_utf8(cursor.into_inner()).expect("invalid utf-8");
+//!     assert_eq!(
+//!         String::from_utf8(cursor.into_inner()).unwrap(),
+//!         "<h1>Title 1</h1><section><p><b>Section 1</b></p></section>\
+//!          <h2>Title 2</h2><section><p><u>Section 2</u></p></section>\
+//!          <h1>Title 3</h1><section><p><i>Section 3</i></p></section>\
+//!          <h1>Title 4</h1><section><p><code>Section 4</code></p></section>"
+//!     );
+//!
+//!     Ok(())
+//! }
 //! ```
 //!
-//! or `impl HtmlHandler` to create your own render. The following example
-//! add an anchor to every headline.
+//! # Custom HtmlHandler
+//!
+//! You can create your own handler by implementing [`HtmlHandler`] trait and passing
+//! it to the [`HtmlRender`].
+//!
+//! The following example demonstrates how to add an anchor for every headline and use
+//! your own error type.
+//!
+//! [`HtmlHandler`]: export/trait.HtmlHandler.html
+//! [`HtmlRender`]: export/struct.HtmlRender.html
 //!
 //! ```rust
-//! use std::io::{Cursor, Error, Result, Write};
-//!
-//! use orgize::export::*;
-//! use orgize::headline::Headline;
+//! use orgize::{export::*, headline::Headline};
 //! use slugify::slugify;
+//! use std::io::{Cursor, Error as IOError, Write};
+//! use std::string::FromUtf8Error;
+//!
+//! // custom error type
+//! #[derive(Debug)]
+//! enum Error {
+//!     IO(IOError),
+//!     Headline,
+//!     Utf8(FromUtf8Error),
+//! }
+//!
+//! // From<std::io::Error> trait is required for custom error type
+//! impl From<IOError> for Error {
+//!     fn from(err: IOError) -> Error {
+//!         Error::IO(err)
+//!     }
+//! }
 //!
 //! struct CustomHtmlHandler;
 //!
 //! impl<W: Write> HtmlHandler<W, Error> for CustomHtmlHandler {
-//!     fn headline_beg(&mut self, w: &mut W, hdl: Headline) -> Result<()> {
-//!         write!(
-//!             w,
-//!             r##"<h{0}><a class="anchor" href="#{1}">{2}</a></h{0}>"##,
-//!             if hdl.level <= 6 { hdl.level } else { 6 },
-//!             slugify!(hdl.title),
-//!             hdl.title,
-//!         )
+//!     fn headline_beg(&mut self, w: &mut W, hdl: Headline) -> Result<(), Error> {
+//!          if hdl.level > 6 {
+//!              Err(Error::Headline)
+//!          } else {
+//!              write!(
+//!                  w,
+//!                  r##"<h{}><a class="anchor" href="#{}">"##,
+//!                  hdl.level,
+//!                  slugify!(hdl.title),
+//!              )?;
+//!              self.escape(w, hdl.title)?;
+//!              Ok(write!(w, "</a></h{}>", hdl.level)?)
+//!          }
 //!     }
 //! }
 //!
-//! let contents = r"* Title 1
+//! fn main() -> Result<(), Error> {
+//!     let contents = r"* Title 1
 //! *Section 1*
 //! ** Title 2
 //! _Section 2_
@@ -79,18 +122,23 @@
 //! * Title 4
 //! =Section 4=";
 //!
-//! let mut cursor = Cursor::new(Vec::new());
+//!     let mut cursor = Cursor::new(Vec::new());
+//!     let mut render = HtmlRender::new(CustomHtmlHandler, &mut cursor, &contents);
 //!
-//! let mut render = HtmlRender::new(CustomHtmlHandler, &mut cursor, &contents);
+//!     render.render()?;
 //!
-//! render
-//!     .render()
-//!     .expect("something went wrong rendering the file");
+//!     assert_eq!(
+//!         String::from_utf8(cursor.into_inner()).map_err(Error::Utf8)?,
+//!         "<h1><a class=\"anchor\" href=\"#title-1\">Title 1</a></h1><section><p><b>Section 1</b></p></section>\
+//!          <h2><a class=\"anchor\" href=\"#title-2\">Title 2</a></h2><section><p><u>Section 2</u></p></section>\
+//!          <h1><a class=\"anchor\" href=\"#title-3\">Title 3</a></h1><section><p><i>Section 3</i></p></section>\
+//!          <h1><a class=\"anchor\" href=\"#title-4\">Title 4</a></h1><section><p><code>Section 4</code></p></section>"
+//!     );
 //!
-//! let result = String::from_utf8(cursor.into_inner()).expect("invalid utf-8");
+//!     Ok(())
+//! }
 //! ```
 
-#[warn(missing_docs)]
 pub mod elements;
 pub mod export;
 pub mod headline;
diff --git a/tests/html.rs b/tests/html.rs
index ec8484c..c5393bb 100644
--- a/tests/html.rs
+++ b/tests/html.rs
@@ -3,20 +3,22 @@ extern crate orgize;
 use orgize::export::HtmlRender;
 use std::io::Cursor;
 
-macro_rules! parse_assert {
-    ($content:expr, $expected:expr) => {{
-        let mut cursor = Cursor::new(Vec::new());
-        let mut render = HtmlRender::default(&mut cursor, $content);
-        render.render().expect("render error");
-        let s = String::from_utf8(cursor.into_inner()).expect("invalid utf-8");
-        assert_eq!(s, $expected);
-    }};
+macro_rules! html_test {
+    ($name:ident, $content:expr, $expected:expr) => {
+        #[test]
+        fn $name() {
+            let mut cursor = Cursor::new(Vec::new());
+            let mut render = HtmlRender::default(&mut cursor, $content);
+            render.render().expect("render error");
+            let s = String::from_utf8(cursor.into_inner()).expect("invalid utf-8");
+            assert_eq!(s, $expected);
+        }
+    };
 }
 
-#[test]
-fn emphasis() {
-    parse_assert!(
-        r#"* Title 1
+html_test!(
+    emphasis,
+    r#"* Title 1
 *Section 1*
 ** Title 2
 _Section 2_
@@ -24,19 +26,15 @@ _Section 2_
 /Section 3/
 * Title 4
 =Section 4="#,
-        concat!(
-            "<h1>Title 1</h1><section><p><b>Section 1</b></p></section>",
-            "<h2>Title 2</h2><section><p><u>Section 2</u></p></section>",
-            "<h1>Title 3</h1><section><p><i>Section 3</i></p></section>",
-            "<h1>Title 4</h1><section><p><code>Section 4</code></p></section>"
-        )
-    )
-}
+    "<h1>Title 1</h1><section><p><b>Section 1</b></p></section>\
+     <h2>Title 2</h2><section><p><u>Section 2</u></p></section>\
+     <h1>Title 3</h1><section><p><i>Section 3</i></p></section>\
+     <h1>Title 4</h1><section><p><code>Section 4</code></p></section>"
+);
 
-#[test]
-fn list() {
-    parse_assert!(
-        r#"+ 1
+html_test!(
+    list,
+    r#"+ 1
 
 + 2
 
@@ -45,12 +43,9 @@ fn list() {
   - 4
 
 + 5"#,
-        concat!(
-            "<section><ul>",
-            "<li><p>1</p></li>",
-            "<li><p>2</p><ul><li><p>3</p></li><li><p>4</p></li></ul></li>",
-            "<li><p>5</p></li>",
-            "</ul></section>"
-        )
-    )
-}
+    "<section><ul>\
+     <li><p>1</p></li>\
+     <li><p>2</p><ul><li><p>3</p></li><li><p>4</p></li></ul></li>\
+     <li><p>5</p></li>\
+     </ul></section>"
+);