diff --git a/src/attribute.rs b/src/attribute.rs
new file mode 100644
index 000000000..4c075e475
--- /dev/null
+++ b/src/attribute.rs
@@ -0,0 +1,105 @@
+use std::fmt;
+
+/// Represent an attribute number along with the word index
+/// according to the tokenizer used.
+///
+/// It can accept up to 1024 attributes and word positions
+/// can be maximum 2^22.
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub struct Attribute(u32);
+
+impl Attribute {
+    /// Construct an `Attribute` from an attribute number and
+    /// the word position of a match according to the tokenizer used.
+    pub(crate) fn new(attribute: u16, index: u32) -> Result<Attribute, AttributeError> {
+        if attribute & 0b1111_1100_0000_0000 != 0 {
+            return Err(AttributeError::AttributeTooBig)
+        }
+
+        if index & 0b1111_1111_1100_0000_0000_0000_0000 != 0 {
+            return Err(AttributeError::IndexTooBig)
+        }
+
+        let attribute = u32::from(attribute) << 22;
+        Ok(Attribute(attribute | index))
+    }
+
+    /// Construct an `Attribute` from an attribute number and
+    /// the word position of a match according to the tokenizer used.
+    ///
+    /// # Panics
+    ///
+    /// The attribute must not be greater than 1024
+    /// and the word index not greater than 2^22.
+    pub(crate) fn new_faillible(attribute: u16, index: u32) -> Attribute {
+        match Attribute::new(attribute, index) {
+            Ok(attribute) => attribute,
+            Err(AttributeError::AttributeTooBig) => {
+                panic!("attribute must not be greater than 1024")
+            },
+            Err(AttributeError::IndexTooBig) => {
+                panic!("attribute word index must not be greater than 2^22")
+            },
+        }
+    }
+
+    pub(crate) fn max_value() -> Attribute {
+        Attribute(u32::max_value())
+    }
+
+    #[inline]
+    pub fn attribute(self) -> u16 {
+        (self.0 >> 22) as u16
+    }
+
+    #[inline]
+    pub fn word_index(self) -> u32 {
+        self.0 & 0b0000_0000_0011_1111_1111_1111_1111
+    }
+}
+
+impl fmt::Debug for Attribute {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.debug_struct("Attribute")
+            .field("attribute", &self.attribute())
+            .field("word_index", &self.word_index())
+            .finish()
+    }
+}
+
+pub enum AttributeError {
+    AttributeTooBig,
+    IndexTooBig,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use quickcheck::{quickcheck, TestResult};
+
+    quickcheck! {
+        fn qc_attribute(gen_attr: u16, gen_index: u32) -> TestResult {
+            if gen_attr > 2_u16.pow(10) || gen_index > 2_u32.pow(22) {
+                return TestResult::discard()
+            }
+
+            let attribute = Attribute::new_faillible(gen_attr, gen_index);
+
+            let valid_attribute = attribute.attribute() == gen_attr;
+            let valid_index = attribute.word_index() == gen_index;
+
+            TestResult::from_bool(valid_attribute && valid_index)
+        }
+
+        fn qc_attribute_ord(gen_attr: u16, gen_index: u32) -> TestResult {
+            if gen_attr >= 2_u16.pow(10) || gen_index >= 2_u32.pow(22) {
+                return TestResult::discard()
+            }
+
+            let a = Attribute::new_faillible(gen_attr, gen_index);
+            let b = Attribute::new_faillible(gen_attr + 1, gen_index + 1);
+
+            TestResult::from_bool(a < b)
+        }
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index 03c2a200d..c7f10d08f 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -5,6 +5,7 @@ pub mod database;
 pub mod data;
 pub mod rank;
 pub mod tokenizer;
+mod attribute;
 mod common_words;
 
 use std::fmt;
@@ -13,6 +14,7 @@ pub use rocksdb;
 
 pub use self::tokenizer::Tokenizer;
 pub use self::common_words::CommonWords;
+pub use self::attribute::{Attribute, AttributeError};
 
 /// Represent an internally generated document unique identifier.
 ///
@@ -21,74 +23,6 @@ pub use self::common_words::CommonWords;
 #[derive(Debug, Copy, Clone, Eq, PartialEq, PartialOrd, Ord, Hash)]
 pub struct DocumentId(u64);
 
-/// Represent an attribute number along with the word index
-/// according to the tokenizer used.
-///
-/// It can accept up to 1024 attributes and word positions
-/// can be maximum 2^22.
-#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
-pub struct Attribute(u32);
-
-impl Attribute {
-    /// Construct an `Attribute` from an attribute number and
-    /// the word position of a match according to the tokenizer used.
-    fn new(attribute: u16, index: u32) -> Result<Attribute, AttributeError> {
-        if attribute & 0b1111_1100_0000_0000 != 0 {
-            return Err(AttributeError::AttributeTooBig)
-        }
-
-        if index & 0b1111_1111_1100_0000_0000_0000_0000 != 0 {
-            return Err(AttributeError::IndexTooBig)
-        }
-
-        let attribute = u32::from(attribute) << 22;
-        Ok(Attribute(attribute | index))
-    }
-
-    /// Construct an `Attribute` from an attribute number and
-    /// the word position of a match according to the tokenizer used.
-    ///
-    /// # Panics
-    ///
-    /// The attribute must not be greater than 1024
-    /// and the word index not greater than 2^22.
-    fn new_faillible(attribute: u16, index: u32) -> Attribute {
-        match Attribute::new(attribute, index) {
-            Ok(attribute) => attribute,
-            Err(AttributeError::AttributeTooBig) => {
-                panic!("attribute must not be greater than 1024")
-            },
-            Err(AttributeError::IndexTooBig) => {
-                panic!("attribute word index must not be greater than 2^22")
-            },
-        }
-    }
-
-    #[inline]
-    pub fn attribute(self) -> u16 {
-        (self.0 >> 22) as u16
-    }
-
-    #[inline]
-    pub fn word_index(self) -> u32 {
-        self.0 & 0b0000_0000_0011_1111_1111_1111_1111
-    }
-}
-
-impl fmt::Debug for Attribute {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        f.debug_struct("Attribute")
-            .field("attribute", &self.attribute())
-            .field("word_index", &self.word_index())
-            .finish()
-    }
-}
-
-enum AttributeError {
-    AttributeTooBig,
-    IndexTooBig,
-}
-
 /// Represent a word position in bytes along with the length of it.
 ///
 /// It can represent words byte index to maximum 2^22 and
@@ -227,7 +161,7 @@ impl Match {
         Match {
             query_index: u32::max_value(),
             distance: u8::max_value(),
-            attribute: Attribute(u32::max_value()),
+            attribute: Attribute::max_value(),
             is_exact: true,
             word_area: WordArea(u32::max_value()),
         }
@@ -246,30 +180,6 @@ mod tests {
     }
 
     quickcheck! {
-        fn qc_attribute(gen_attr: u16, gen_index: u32) -> TestResult {
-            if gen_attr > 2_u16.pow(10) || gen_index > 2_u32.pow(22) {
-                return TestResult::discard()
-            }
-
-            let attribute = Attribute::new_faillible(gen_attr, gen_index);
-
-            let valid_attribute = attribute.attribute() == gen_attr;
-            let valid_index = attribute.word_index() == gen_index;
-
-            TestResult::from_bool(valid_attribute && valid_index)
-        }
-
-        fn qc_attribute_ord(gen_attr: u16, gen_index: u32) -> TestResult {
-            if gen_attr >= 2_u16.pow(10) || gen_index >= 2_u32.pow(22) {
-                return TestResult::discard()
-            }
-
-            let a = Attribute::new_faillible(gen_attr, gen_index);
-            let b = Attribute::new_faillible(gen_attr + 1, gen_index + 1);
-
-            TestResult::from_bool(a < b)
-        }
-
         fn qc_word_area(gen_char_index: u32, gen_length: u16) -> TestResult {
             if gen_char_index > 2_u32.pow(22) || gen_length > 2_u16.pow(10) {
                 return TestResult::discard()