diff --git a/src/bits.rs b/src/bits.rs
index 022ad37..5d1f93f 100644
--- a/src/bits.rs
+++ b/src/bits.rs
@@ -99,6 +99,12 @@ impl Bits {
 
     /// The maximum number of bits allowed by the provided QR code version and
     /// error correction level.
+    ///
+    /// # Errors
+    ///
+    /// Returns `Err(QrError::InvalidVersion)` if it is not valid to use the
+    /// `ec_level` for the given version (e.g. `Version::Micro(1)` with
+    /// `EcLevel::H`).
     pub fn max_len(&self, ec_level: EcLevel) -> QrResult<usize> {
         self.version.fetch(ec_level, &DATA_LENGTHS)
     }
@@ -179,6 +185,8 @@ pub enum ExtendedMode {
 impl Bits {
     /// Push the mode indicator to the end of the bits.
     ///
+    /// # Errors
+    ///
     /// If the mode is not supported in the provided version, this method
     /// returns `Err(QrError::UnsupportedCharacterSet)`.
     pub fn push_mode_indicator(&mut self, mode: ExtendedMode) -> QrResult<()> {
@@ -239,6 +247,8 @@ impl Bits {
     /// 29    | GB-18030 (Simplified Chinese)
     /// 30    | EUC-KR (Korean)
     ///
+    /// # Errors
+    ///
     /// If the QR code version does not support ECI, this method will return
     /// `Err(QrError::UnsupportedCharacterSet)`.
     ///
@@ -321,6 +331,10 @@ impl Bits {
     /// Encodes a numeric string to the bits.
     ///
     /// The data should only contain the characters 0 to 9.
+    ///
+    /// # Errors
+    ///
+    /// Returns `Err(QrError::DataTooLong)` on overflow.
     pub fn push_numeric_data(&mut self, data: &[u8]) -> QrResult<()> {
         self.push_header(Mode::Numeric, data.len())?;
         for chunk in data.chunks(3) {
@@ -425,6 +439,10 @@ impl Bits {
     ///
     /// The data should only contain the charaters A to Z (excluding lowercase),
     /// 0 to 9, space, `$`, `%`, `*`, `+`, `-`, `.`, `/` or `:`.
+    ///
+    /// # Errors
+    ///
+    /// Returns `Err(QrError::DataTooLong)` on overflow.
     pub fn push_alphanumeric_data(&mut self, data: &[u8]) -> QrResult<()> {
         self.push_header(Mode::Alphanumeric, data.len())?;
         for chunk in data.chunks(2) {
@@ -470,6 +488,10 @@ mod alphanumeric_tests {
 
 impl Bits {
     /// Encodes 8-bit byte data to the bits.
+    ///
+    /// # Errors
+    ///
+    /// Returns `Err(QrError::DataTooLong)` on overflow.
     pub fn push_byte_data(&mut self, data: &[u8]) -> QrResult<()> {
         self.push_header(Mode::Byte, data.len())?;
         for b in data {
@@ -524,6 +546,13 @@ mod byte_tests {
 
 impl Bits {
     /// Encodes Shift JIS double-byte data to the bits.
+    ///
+    /// # Errors
+    ///
+    /// Returns `Err(QrError::DataTooLong)` on overflow.
+    ///
+    /// Returns `Err(QrError::InvalidCharacter)` if the data is not Shift JIS
+    /// double-byte data (e.g. if the length of data is not an even number).
     pub fn push_kanji_data(&mut self, data: &[u8]) -> QrResult<()> {
         self.push_header(Mode::Kanji, data.len() / 2)?;
         for kanji in data.chunks(2) {
@@ -583,6 +612,11 @@ impl Bits {
     ///     bits.push_alphanumeric_data(b"%10ABC123");
     ///
     /// In QR code, the character `%` is used as the data field separator (0x1D).
+    ///
+    /// # Errors
+    ///
+    /// If the mode is not supported in the provided version, this method
+    /// returns `Err(QrError::UnsupportedCharacterSet)`.
     pub fn push_fnc1_first_position(&mut self) -> QrResult<()> {
         self.push_mode_indicator(ExtendedMode::Fnc1First)
     }
@@ -607,6 +641,11 @@ impl Bits {
     /// ```ignore
     /// bits.push_fnc1_second_position(b'A' + 100);
     /// ```
+    ///
+    /// # Errors
+    ///
+    /// If the mode is not supported in the provided version, this method
+    /// returns `Err(QrError::UnsupportedCharacterSet)`.
     pub fn push_fnc1_second_position(&mut self, application_indicator: u8) -> QrResult<()> {
         self.push_mode_indicator(ExtendedMode::Fnc1Second)?;
         self.push_number(8, u16::from(application_indicator));
@@ -670,6 +709,14 @@ static DATA_LENGTHS: [[usize; 4]; 44] = [
 
 impl Bits {
     /// Pushes the ending bits to indicate no more data.
+    ///
+    /// # Errors
+    ///
+    /// Returns `Err(QrError::DataTooLong)` on overflow.
+    ///
+    /// Returns `Err(QrError::InvalidVersion)` if it is not valid to use the
+    /// `ec_level` for the given version (e.g. `Version::Micro(1)` with
+    /// `EcLevel::H`).
     pub fn push_terminator(&mut self, ec_level: EcLevel) -> QrResult<()> {
         let terminator_size = match self.version {
             Version::Micro(a) => a.as_usize() * 2 + 1,
@@ -770,6 +817,13 @@ mod finish_tests {
 
 impl Bits {
     /// Push a segmented data to the bits, and then terminate it.
+    ///
+    /// # Errors
+    ///
+    /// Returns `Err(QrError::DataTooLong)` on overflow.
+    ///
+    /// Returns `Err(QrError::InvalidData)` if the segment refers to incorrectly
+    /// encoded byte sequence.
     pub fn push_segments<I>(&mut self, data: &[u8], segments_iter: I) -> QrResult<()>
     where
         I: Iterator<Item = Segment>,
@@ -787,6 +841,10 @@ impl Bits {
     }
 
     /// Pushes the data the bits, using the optimal encoding.
+    ///
+    /// # Errors
+    ///
+    /// Returns `Err(QrError::DataTooLong)` on overflow.
     pub fn push_optimal_data(&mut self, data: &[u8]) -> QrResult<()> {
         let segments = Parser::new(data).optimize(self.version);
         self.push_segments(data, segments)
@@ -838,6 +896,11 @@ mod encode_tests {
 /// the result.
 ///
 /// This method will not consider any Micro QR code versions.
+///
+/// # Errors
+///
+/// Returns `Err(QrError::DataTooLong)` if the data is too long to fit even the
+/// highest QR code version.
 pub fn encode_auto(data: &[u8], ec_level: EcLevel) -> QrResult<Bits> {
     let segments = Parser::new(data).collect::<Vec<Segment>>();
     for version in &[Version::Normal(9), Version::Normal(26), Version::Normal(40)] {
diff --git a/src/ec.rs b/src/ec.rs
index dbe9594..857de08 100644
--- a/src/ec.rs
+++ b/src/ec.rs
@@ -98,6 +98,12 @@ fn test_interleave() {
 
 /// Constructs data and error correction codewords ready to be put in the QR
 /// code matrix.
+///
+/// # Errors
+///
+/// Returns `Err(QrError::InvalidVersion)` if it is not valid to use the
+///  `ec_level` for the given version (e.g. `Version::Micro(1)` with
+/// `EcLevel::H`).
 pub fn construct_codewords(rawbits: &[u8], version: Version, ec_level: EcLevel) -> QrResult<(Vec<u8>, Vec<u8>)> {
     let (block_1_size, block_1_count, block_2_size, block_2_count) = version.fetch(ec_level, &DATA_BYTES_PER_BLOCK)?;
 
@@ -162,6 +168,12 @@ mod construct_codewords_test {
 
 /// Computes the maximum allowed number of erratic modules can be introduced to
 /// the QR code, before the data becomes truly corrupted.
+///
+/// # Errors
+///
+/// Returns `Err(QrError::InvalidVersion)` if it is not valid to use the
+///  `ec_level` for the given version (e.g. `Version::Micro(1)` with
+/// `EcLevel::H`).
 pub fn max_allowed_errors(version: Version, ec_level: EcLevel) -> QrResult<usize> {
     use crate::EcLevel::{L, M};
     use crate::Version::{Micro, Normal};
diff --git a/src/lib.rs b/src/lib.rs
index 4edb565..b748659 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -14,7 +14,9 @@
 //! let image = code.render::<Luma<u8>>().build();
 //!
 //! // Save the image.
+//! # if cfg!(unix) {
 //! image.save("/tmp/qrcode.png").unwrap();
+//! # }
 //!
 //! // You can also render it into a string.
 //! let string = code.render()
@@ -68,6 +70,10 @@ impl QrCode {
     ///
     ///     let code = QrCode::new(b"Some data").unwrap();
     ///
+    /// # Errors
+    ///
+    /// Returns error if the QR code cannot be constructed, e.g. when the data
+    /// is too long.
     pub fn new<D: AsRef<[u8]>>(data: D) -> QrResult<Self> {
         Self::with_error_correction_level(data, EcLevel::M)
     }
@@ -81,6 +87,10 @@ impl QrCode {
     ///
     ///     let code = QrCode::with_error_correction_level(b"Some data", EcLevel::H).unwrap();
     ///
+    /// # Errors
+    ///
+    /// Returns error if the QR code cannot be constructed, e.g. when the data
+    /// is too long.
     pub fn with_error_correction_level<D: AsRef<[u8]>>(data: D, ec_level: EcLevel) -> QrResult<Self> {
         let bits = bits::encode_auto(data.as_ref(), ec_level)?;
         Self::with_bits(bits, ec_level)
@@ -99,6 +109,11 @@ impl QrCode {
     ///
     ///     let micro_code = QrCode::with_version(b"123", Version::Micro(1), EcLevel::L).unwrap();
     ///
+    /// # Errors
+    ///
+    /// Returns error if the QR code cannot be constructed, e.g. when the data
+    /// is too long, or when the version and error correction level are
+    /// incompatible.
     pub fn with_version<D: AsRef<[u8]>>(data: D, version: Version, ec_level: EcLevel) -> QrResult<Self> {
         let mut bits = bits::Bits::new(version);
         bits.push_optimal_data(data.as_ref())?;
@@ -128,6 +143,11 @@ impl QrCode {
     ///     bits.push_terminator(EcLevel::L);
     ///     let qrcode = QrCode::with_bits(bits, EcLevel::L);
     ///
+    /// # Errors
+    ///
+    /// Returns error if the QR code cannot be constructed, e.g. when the bits
+    /// are too long, or when the version and error correction level are
+    /// incompatible.
     pub fn with_bits(bits: bits::Bits, ec_level: EcLevel) -> QrResult<Self> {
         let version = bits.version();
         let data = bits.into_bytes();
diff --git a/src/render/unicode.rs b/src/render/unicode.rs
index 060066c..4ae97b8 100644
--- a/src/render/unicode.rs
+++ b/src/render/unicode.rs
@@ -22,14 +22,14 @@ impl Pixel for Dense1x2 {
 }
 
 impl Dense1x2 {
-    fn value(&self) -> u8 {
+    fn value(self) -> u8 {
         match self {
             Dense1x2::Dark => 1,
             Dense1x2::Light => 0,
         }
     }
-    fn parse_2_bits(sym: &u8) -> &'static str {
-        CODEPAGE[*sym as usize]
+    fn parse_2_bits(sym: u8) -> &'static str {
+        CODEPAGE[usize::from(sym)]
     }
 }
 
@@ -68,7 +68,7 @@ impl RenderCanvas for Canvas1x2 {
                         rows[0].iter().map(|top| (top * 2)).collect::<Vec<u8>>()
                     }
                 }
-                .iter()
+                .into_iter()
                 // Mapping those 2-bit numbers to corresponding pixels.
                 .map(Dense1x2::parse_2_bits)
                 .collect::<Vec<&str>>()
diff --git a/src/types.rs b/src/types.rs
index 22c7e6f..95a716c 100644
--- a/src/types.rs
+++ b/src/types.rs
@@ -146,7 +146,9 @@ impl Version {
     /// inner array represents the content in each error correction level, in
     /// the order [L, M, Q, H].
     ///
-    /// If the entry compares equal to the default value of T, this method
+    /// # Errors
+    ///
+    /// If the entry compares equal to the default value of `T`, this method
     /// returns `Err(QrError::InvalidVersion)`.
     pub fn fetch<T>(self, ec_level: EcLevel, table: &[[T; 4]]) -> QrResult<T>
     where