diff --git a/src/exporter/mod.rs b/src/exporter/mod.rs
index 4f9244a..3161c68 100644
--- a/src/exporter/mod.rs
+++ b/src/exporter/mod.rs
@@ -49,5 +49,5 @@ pub trait ElementSerializer {
     /// Performs the serialization.
     ///
     /// Writes the serialization on the output and returns Err if an error occured.
-    fn serialize<W: Write>(&self, element: Element, output: &mut W) -> Result<(), ExportError>;
+    fn serialize<W: Write>(&self, element: Element, output: &mut W) -> Result<usize, ExportError>;
 }
diff --git a/src/exporter/obj.rs b/src/exporter/obj.rs
index a33813b..167ce10 100644
--- a/src/exporter/obj.rs
+++ b/src/exporter/obj.rs
@@ -24,31 +24,31 @@ impl ObjElementSerializer {
     }
 
     /// Writes a face to a writable output.
-    pub fn write_face<W: Write>(&self, f: model::Face, output: &mut W) -> Result<(), ExportError> {
+    pub fn face_to_string(&self, f: model::Face) -> String {
+
         if f.a.texture_coordinate.is_none() && f.a.normal.is_none() {
             // Only vertices
-            writeln!(output, "f {} {} {}", f.a.vertex + 1, f.b.vertex + 1, f.c.vertex + 1)?;
+            format!("f {} {} {}", f.a.vertex + 1, f.b.vertex + 1, f.c.vertex + 1)
         } else if f.a.normal.is_none() {
             // Vertices + tex coords
-            writeln!(output, "f {}/{} {}/{} {}/{}",
+            format!("f {}/{} {}/{} {}/{}",
                    f.a.vertex + 1, f.a.texture_coordinate.unwrap() + 1,
                    f.b.vertex + 1, f.b.texture_coordinate.unwrap() + 1,
-                   f.c.vertex + 1, f.c.texture_coordinate.unwrap() + 1)?;
+                   f.c.vertex + 1, f.c.texture_coordinate.unwrap() + 1)
         } else if f.a.texture_coordinate.is_none() {
             // Vertices + normals
-            writeln!(output, "f {}//{} {}//{} {}//{}",
+            format!("f {}//{} {}//{} {}//{}",
                    f.a.vertex + 1, f.a.normal.unwrap() + 1,
                    f.b.vertex + 1, f.b.normal.unwrap() + 1,
-                   f.c.vertex + 1, f.c.normal.unwrap() + 1)?;
+                   f.c.vertex + 1, f.c.normal.unwrap() + 1)
         } else {
             // All
-            writeln!(output, "f {}/{}/{} {}/{}/{} {}/{}/{}",
+            format!("f {}/{}/{} {}/{}/{} {}/{}/{}",
                    f.a.vertex + 1, f.a.texture_coordinate.unwrap() + 1, f.a.normal.unwrap() + 1,
                    f.b.vertex + 1, f.b.texture_coordinate.unwrap() + 1, f.b.normal.unwrap() + 1,
-                   f.c.vertex + 1, f.c.texture_coordinate.unwrap() + 1, f.c.normal.unwrap() + 1)?;
+                   f.c.vertex + 1, f.c.texture_coordinate.unwrap() + 1, f.c.normal.unwrap() + 1)
         }
 
-        Ok(())
     }
 }
 
@@ -67,17 +67,18 @@ impl ElementSerializer for ObjElementSerializer {
     /// let result = String::from_utf8(output).unwrap();
     /// assert_eq!(result, "v 1 2 3\n");
     /// ```
-    fn serialize<W: Write>(&self, element: Element, output: &mut W) -> Result<(), ExportError> {
+    fn serialize<W: Write>(&self, element: Element, output: &mut W) -> Result<usize, ExportError> {
 
-        match element {
-            Vertex(v) => writeln!(output, "v {} {} {}", v.x(), v.y(), v.z())?,
-            TextureCoordinate(vt) => writeln!(output, "vt {} {}", vt.x(), vt.y())?,
-            Normal(n) => writeln!(output, "vn {} {} {}", n.x(), n.y(), n.z())?,
-            Face(f) => self.write_face(f, output)?,
-            UseMaterial(ref n) => writeln!(output, "usemtl {}", n)?,
-            _ => (),
-        }
+        let string = match element {
+            Vertex(v) => format!("v {} {} {}", v.x(), v.y(), v.z()),
+            TextureCoordinate(vt) => format!("vt {} {}", vt.x(), vt.y()),
+            Normal(n) => format!("vn {} {} {}", n.x(), n.y(), n.z()),
+            Face(f) => self.face_to_string(f),
+            UseMaterial(ref n) => format!("usemtl {}", n),
+            _ => return Ok(0),
+        };
 
-        Ok(())
+        writeln!(output, "{}", string)?;
+        Ok(string.len() + 1)
     }
 }
diff --git a/src/math/vector.rs b/src/math/vector.rs
index de72689..699958f 100644
--- a/src/math/vector.rs
+++ b/src/math/vector.rs
@@ -112,6 +112,11 @@ macro_rules! make_vector {
                 *self /= self.norm()
             }
 
+            /// Returns a new normalized vector.
+            pub fn normalized(&self) -> $name<T> {
+                *self / self.norm()
+            }
+
         }
 
         impl<T: Number> Add for $name<T> {
@@ -224,6 +229,7 @@ make_vector!(Vector3, 3, (T, T, T), (x, x_mut, 0), (y, y_mut, 1), (z, z_mut, 2))
 make_vector!(Vector4, 4, (T, T, T, T), (x, x_mut, 0), (y, y_mut, 1), (z, z_mut, 2), (t, t_mut, 3));
 
 impl Vector2<f32> {
+    /// Returns a orthogonal vector to the one passed as parameter.
     pub fn orthogonal(&self) -> Vector2<f32> {
         Vector2::new(
             self.y(),
@@ -233,6 +239,7 @@ impl Vector2<f32> {
 }
 
 impl Vector2<i32> {
+    /// Returns a orthogonal vector to the one passed as parameter.
     pub fn orthogonal(&self) -> Vector2<i32> {
         Vector2::new(
             self.y(),
diff --git a/src/parser/mod.rs b/src/parser/mod.rs
index c0d6981..ccb158b 100644
--- a/src/parser/mod.rs
+++ b/src/parser/mod.rs
@@ -175,6 +175,9 @@ pub trait Parser {
         self.priv_parse_into_model(model, path)
     }
 
+    /// Parses a file and adds its content to an already existing model.
+    ///
+    /// This is the method you should implement for you format parser.
     fn priv_parse_into_model(&mut self, model: &mut Model, path: &str) -> Result<(), ParserError>;
 }
 
@@ -205,6 +208,8 @@ impl<LP: LineParser> Parser for LP {
         use std::io::BufRead;
         for (num, line) in file.lines().enumerate() {
 
+            let num = num + 1;
+
             if line.is_err() {
                 return Err(ParserError::OtherError(path.to_owned()));
             }