diff --git a/README.md b/README.md
index 80d990d..59d08c2 100644
--- a/README.md
+++ b/README.md
@@ -21,7 +21,7 @@ use estring::{SepVec, EString};
 type PlusVec<T> = SepVec<T, '+'>;
 type MulVec<T> = SepVec<T, '*'>;
 
-fn main() -> Result<(), estring::ParseError> {
+fn main() -> estring::Result<()> {
     let res = EString::from("10+5*2+3")
         .parse::<PlusVec<MulVec<f32>>>()?
         .iter()
@@ -33,14 +33,15 @@ fn main() -> Result<(), estring::ParseError> {
 }
 ```
 
-You can use custom types as annotations! Just implement `TryFrom<EString>`!
+You can use custom types as annotations! Just implement
+`estring::ParseFragment`!
 
 ## Installation
 
 **The MSRV is 1.59.0**
 
-Add `estring = { version = "0.1", features = ["vec", "number"] }` as a
-dependency in `Cargo.toml`.
+Add `estring = { version = "0.1", features = ["structs"] }` as a dependency in
+`Cargo.toml`.
 
 `Cargo.toml` example:
 
@@ -52,7 +53,7 @@ edition = "2021"
 authors = ["Me <user@rust-lang.org>"]
 
 [dependencies]
-estring = { version = "0.1", features = ["vec", "number"] }
+estring = { version = "0.1", features = ["structs"] }
 ```
 
 ## License
diff --git a/examples/calc.rs b/examples/calc.rs
index 27ea9e4..2799242 100644
--- a/examples/calc.rs
+++ b/examples/calc.rs
@@ -3,7 +3,7 @@ use estring::{EString, SepVec};
 type PlusVec<T> = SepVec<T, '+'>;
 type MulVec<T> = SepVec<T, '*'>;
 
-fn main() -> Result<(), estring::ParseError> {
+fn main() -> estring::Result<()> {
     let res = EString::from("10+5*2+3")
         .parse::<PlusVec<MulVec<f32>>>()?
         .iter()
diff --git a/examples/dotenv.rs b/examples/dotenv.rs
index a13d441..dee7a0a 100644
--- a/examples/dotenv.rs
+++ b/examples/dotenv.rs
@@ -5,7 +5,7 @@ DATABASE_URL=postgres://user:password@localhost:5432/recipes
 APP_HOST=http://localhost:3000
 ";
 
-fn main() -> Result<(), estring::ParseError> {
+fn main() -> estring::Result<()> {
     EString::from(DOTENV_CONTENT)
         .parse::<Trim<SepVec<Pair<&str, '=', &str>, '\n'>>>()?
         .iter()
diff --git a/src/core.rs b/src/core.rs
index f4bc8f9..ef570ab 100644
--- a/src/core.rs
+++ b/src/core.rs
@@ -2,8 +2,73 @@
 //! string types
 //!
 
-use crate::ParseError;
-use std::convert::Infallible;
+// TODO: add more info and examples.
+/// Format a value fragment into a ``EString``.
+pub trait FormatFragment {
+    /// Format this type and returns ``EString``.
+    fn fmt_frag(&self) -> EString;
+}
+
+/// Parse a value fragment from a ``EString``.
+///
+/// ``ParseFragment``’s `parse_frag` method is often used imlicitly, through ``EString``’s parse.
+/// See [parse](EString::parse)’s documentation for examples.
+///
+/// # Examples
+///
+/// Basic implementation of ``ParseFragment`` on an example ``Point``.
+///
+/// ```rust
+/// use estring::{EString, ParseFragment, Reason};
+///
+/// #[derive(Debug, PartialEq)]
+/// struct Point {
+///     x: i32,
+///     y: i32,
+/// }
+///
+/// impl ParseFragment for Point {
+///     fn parse_frag(es: EString) -> estring::Result<Self> {
+///         let orig = es.clone();
+///         let (x, y) = es
+///             .trim_matches(|p| p == '(' || p == ')')
+///             .split_once(',')
+///             .ok_or(estring::Error(orig, Reason::Split))?;
+///
+///         let (x, y) = (EString::from(x), EString::from(y));
+///         let x = x.clone().parse::<i32>()
+///             .map_err(|_| estring::Error(x, Reason::Parse))?;
+///         let y = y.clone().parse::<i32>()
+///             .map_err(|_| estring::Error(y, Reason::Parse))?;
+///
+///         Ok(Point { x, y })
+///     }
+/// }
+///
+/// let fragment = EString::from("(1,2)");
+/// let res = Point::parse_frag(fragment).unwrap();
+/// assert_eq!(res, Point { x: 1, y: 2 })
+/// ```
+///
+pub trait ParseFragment: Sized {
+    /// Parses a ``EString`` fragment `es` to return a value of this type.
+    ///
+    /// # Errors
+    ///
+    /// If parsing is not succeeds, returns ``Error`` inside ``Err`` with original fragment `es`
+    /// and reason ``Reason``.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use estring::{EString, ParseFragment};
+    ///
+    /// let fragment = EString::from("5");
+    /// let res = i32::parse_frag(fragment).unwrap();
+    /// assert_eq!(res, 5);
+    /// ```
+    fn parse_frag(es: EString) -> crate::Result<Self>;
+}
 
 /// Wrapper under String type.
 #[derive(Debug, Default, PartialEq, Eq, Clone)]
@@ -17,9 +82,8 @@ impl EString {
     /// Will return `Err` if estring cannot parse inner fragment
     ///
     #[inline]
-    pub fn parse<T: TryFrom<EString>>(self) -> Result<T, ParseError> {
-        let orig = self.0.clone();
-        <T as TryFrom<EString>>::try_from(self).map_err(|_| ParseError(orig))
+    pub fn parse<T: ParseFragment>(self) -> crate::Result<T> {
+        T::parse_frag(self)
     }
 }
 
@@ -42,20 +106,23 @@ impl std::ops::Deref for EString {
     }
 }
 
-impl TryFrom<EString> for String {
-    type Error = Infallible;
-
+impl ParseFragment for EString {
     #[inline]
-    fn try_from(s: EString) -> Result<Self, Self::Error> {
+    fn parse_frag(value: EString) -> crate::Result<Self> {
+        Ok(value)
+    }
+}
+
+impl ParseFragment for String {
+    #[inline]
+    fn parse_frag(s: EString) -> crate::Result<Self> {
         Ok(s.0)
     }
 }
 
-impl TryFrom<EString> for &'static str {
-    type Error = Infallible;
-
+impl ParseFragment for &'static str {
     #[inline]
-    fn try_from(s: EString) -> Result<Self, Self::Error> {
+    fn parse_frag(s: EString) -> crate::Result<Self> {
         Ok(Box::leak(s.0.into_boxed_str()))
     }
 }
diff --git a/src/error.rs b/src/error.rs
index a484b68..3d99596 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -1,16 +1,31 @@
-/// Failed to parse the specified string.
-#[derive(Debug)]
-pub struct ParseError(pub String);
+use crate::core::EString;
 
-impl std::fmt::Display for ParseError {
+/// The error type for operations interacting with ``EString``’s fragments.
+#[derive(Debug)]
+pub struct Error(pub EString, pub Reason);
+
+/// The reason for the failure to parse.
+#[derive(Debug, PartialEq, Eq)]
+pub enum Reason {
+    /// Cannot split fragment
+    Split,
+    /// Cannot parse fragment
+    Parse,
+}
+
+impl std::fmt::Display for Error {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        write!(f, r#"Failed to parse: "{}""#, self.0)
+        write!(
+            f,
+            r#"Failed to parse "{:?}" with reason {:?}"#,
+            self.0, self.1
+        )
     }
 }
 
-impl std::error::Error for ParseError {}
+impl std::error::Error for Error {}
 
-impl std::ops::Deref for ParseError {
+impl std::ops::Deref for Error {
     type Target = String;
 
     fn deref(&self) -> &Self::Target {
diff --git a/src/lib.rs b/src/lib.rs
index c056c99..73d8637 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -15,7 +15,7 @@
 //! type PlusVec<T> = SepVec<T, '+'>;
 //! type MulVec<T> = SepVec<T, '*'>;
 //!
-//! fn main() -> Result<(), estring::ParseError> {
+//! fn main() -> estring::Result<()> {
 //!     let res = EString::from("10+5*2+3")
 //!         .parse::<PlusVec<MulVec<f32>>>()?
 //!         .iter()
@@ -32,6 +32,43 @@
 #![warn(missing_docs)]
 
 mod error;
+pub use error::{Error, Reason};
+/// The type returned by parser methods.
+///
+/// # Examples
+///
+/// ```rust
+/// use estring::{EString, ParseFragment, Reason};
+///
+/// #[derive(Debug, PartialEq)]
+/// struct Point {
+///     x: i32,
+///     y: i32,
+/// }
+///
+/// impl ParseFragment for Point {
+///     fn parse_frag(es: EString) -> estring::Result<Self> {
+///         let orig = es.clone();
+///         let (x, y) = es
+///             .trim_matches(|p| p == '(' || p == ')')
+///             .split_once(',')
+///             .ok_or(estring::Error(orig, Reason::Split))?;
+///
+///         let (x, y) = (EString::from(x), EString::from(y));
+///         let x = x.clone().parse::<i32>()
+///             .map_err(|_| estring::Error(x, Reason::Parse))?;
+///         let y = y.clone().parse::<i32>()
+///             .map_err(|_| estring::Error(y, Reason::Parse))?;
+///
+///         Ok(Point { x, y })
+///     }
+/// }
+///
+/// let fragment = EString::from("(1,2)");
+/// let res = Point::parse_frag(fragment).unwrap();
+/// assert_eq!(res, Point { x: 1, y: 2 })
+/// ```
+pub type Result<T> = ::std::result::Result<T, Error>;
 
 pub mod core;
 pub mod std;
@@ -51,4 +88,3 @@ pub mod structs;
 pub use structs::*;
 
 pub use crate::core::*;
-pub use crate::error::ParseError;
diff --git a/src/low/trim.rs b/src/low/trim.rs
index f2b32e6..224826c 100644
--- a/src/low/trim.rs
+++ b/src/low/trim.rs
@@ -1,4 +1,4 @@
-use crate::core::EString;
+use crate::{core::EString, ParseFragment};
 
 /// Wrapper that allow to trim substring before continue
 ///
@@ -9,7 +9,7 @@ use crate::core::EString;
 /// ```rust
 /// use estring::{EString, Trim};
 ///
-/// fn main() -> Result<(), estring::ParseError> {
+/// fn main() -> estring::Result<()> {
 ///     let res = EString::from(" 99 ").parse::<Trim<i32>>()?;
 ///     assert_eq!(res, Trim(99));
 ///     Ok(())
@@ -33,16 +33,12 @@ impl<T: std::fmt::Display> std::fmt::Display for Trim<T> {
     }
 }
 
-impl<T> TryFrom<EString> for Trim<T>
+impl<T> ParseFragment for Trim<T>
 where
-    T: TryFrom<EString>,
+    T: ParseFragment,
 {
-    type Error = ();
-
-    fn try_from(value: EString) -> Result<Self, Self::Error> {
-        T::try_from(EString::from(value.trim()))
-            .map(Trim)
-            .map_err(|_| ())
+    fn parse_frag(value: EString) -> crate::Result<Self> {
+        T::parse_frag(EString::from(value.trim())).map(Trim)
     }
 }
 
@@ -60,7 +56,6 @@ mod tests {
         }
     }
 
-    #[cfg(feature = "number")]
     #[test]
     fn should_trim_and_convert_to_number() {
         let estr = EString::from("    999   ");
diff --git a/src/std/bool.rs b/src/std/bool.rs
index c67be8e..0edf4ae 100644
--- a/src/std/bool.rs
+++ b/src/std/bool.rs
@@ -1,14 +1,13 @@
-use crate::core::EString;
-
-impl TryFrom<EString> for bool {
-    type Error = ();
+use crate::core::{EString, ParseFragment};
+use crate::error::{Error, Reason};
 
+impl ParseFragment for bool {
     #[inline]
-    fn try_from(s: EString) -> Result<Self, Self::Error> {
+    fn parse_frag(s: EString) -> crate::Result<Self> {
         match s.to_lowercase().as_str() {
             "true" | "t" | "yes" | "y" | "on" | "1" => Ok(true),
             "false" | "f" | "no" | "n" | "off" | "0" | "" => Ok(false),
-            _ => Err(()),
+            _ => Err(Error(s, Reason::Parse)),
         }
     }
 }
@@ -16,7 +15,6 @@ impl TryFrom<EString> for bool {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::ParseError;
 
     #[test]
     fn should_parse_bool_variable() {
@@ -47,8 +45,9 @@ mod tests {
     fn should_throw_parse_error() {
         let estr = EString::from("something");
         match estr.parse::<bool>() {
-            Err(ParseError(orig)) => {
-                assert_eq!(orig, String::from("something"));
+            Err(crate::Error(orig, reason)) => {
+                assert_eq!(orig, EString::from("something"));
+                assert_eq!(reason, crate::Reason::Parse);
             }
             _ => unreachable!(),
         };
diff --git a/src/std/number.rs b/src/std/number.rs
index 0a3d034..555ebb8 100644
--- a/src/std/number.rs
+++ b/src/std/number.rs
@@ -1,15 +1,14 @@
-use crate::core::EString;
+use crate::core::{EString, ParseFragment};
+use crate::error::{Error, Reason};
 
 #[doc(hidden)]
 macro_rules! from_env_string_numbers_impl {
     ($($ty:ty),+$(,)?) => {
         $(
-            impl TryFrom<EString> for $ty {
-                type Error = <$ty as std::str::FromStr>::Err;
-
+            impl ParseFragment for $ty {
                 #[inline]
-                fn try_from(s: EString) -> Result<Self, Self::Error> {
-                    s.0.parse::<Self>()
+                fn parse_frag(s: EString) -> crate::Result<Self> {
+                    s.0.parse::<Self>().map_err(|_| Error(s, Reason::Parse))
                 }
             }
         )+
@@ -26,7 +25,6 @@ from_env_string_numbers_impl![
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::ParseError;
 
     #[test]
     fn should_parse_number() {
@@ -51,8 +49,9 @@ mod tests {
     fn should_throw_parse_error() {
         let estr = EString::from("-10");
         match estr.parse::<u32>() {
-            Err(ParseError(orig)) => {
-                assert_eq!(orig, String::from("-10"));
+            Err(Error(orig, reason)) => {
+                assert_eq!(orig, EString::from("-10"));
+                assert_eq!(reason, Reason::Parse);
             }
             _ => unreachable!(),
         };
diff --git a/src/structs/pair.rs b/src/structs/pair.rs
index 5c70305..40911cc 100644
--- a/src/structs/pair.rs
+++ b/src/structs/pair.rs
@@ -1,34 +1,13 @@
 //! Contains the implementations to pair tuple type
 //!
 
-use crate::core::EString;
+use crate::core::{EString, ParseFragment};
+use crate::{Error, Reason};
 use std::fmt::Write;
 
-/// The error type for operations interacting with parsing tuples. Possibly returned from
-/// ``EString::parse``
-#[derive(Debug)]
-pub enum Error {
-    /// The specified input string is not split.
-    Split,
-
-    /// The specified substring of the split input string is not parsed
-    Parse(u8),
-}
-
-impl std::fmt::Display for Error {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        match self {
-            Error::Split => f.write_str("Cannot split input string"),
-            Error::Parse(n) => write!(f, "Cannot parse {} substring", n),
-        }
-    }
-}
-
-impl std::error::Error for Error {}
-
 /// Wrapper for pair (A, B) tuple to split string by a separator (`S1`).
 ///
-/// **NOTE**: Required the enabling of the `tuple` feature.
+/// **NOTE**: Required the enabling of the `structs` feature.
 ///
 /// # Examples
 ///
@@ -37,7 +16,7 @@ impl std::error::Error for Error {}
 ///
 /// type EqPair<A, B> = Pair<A, '=', B>;
 ///
-/// fn main() -> Result<(), estring::ParseError> {
+/// fn main() -> estring::Result<()> {
 ///     let res = EString::from("one=two=free").parse::<EqPair<&str, &str>>()?;
 ///     assert_eq!(res, Pair("one", "two=free"));
 ///     Ok(())
@@ -66,19 +45,22 @@ where
     }
 }
 
-impl<A, const S1: char, B> TryFrom<EString> for Pair<A, S1, B>
+impl<A, const S1: char, B> ParseFragment for Pair<A, S1, B>
 where
-    A: TryFrom<EString>,
-    B: TryFrom<EString>,
+    A: ParseFragment,
+    B: ParseFragment,
 {
-    type Error = Error;
-
-    fn try_from(value: EString) -> Result<Self, Self::Error> {
-        value.split_once(S1).ok_or(Error::Split).and_then(|(a, b)| {
-            let a = A::try_from(EString::from(a)).map_err(|_| Error::Parse(0))?;
-            let b = B::try_from(EString::from(b)).map_err(|_| Error::Parse(1))?;
-            Ok(Self(a, b))
-        })
+    fn parse_frag(value: EString) -> crate::Result<Self> {
+        value
+            .clone()
+            .split_once(S1)
+            .ok_or(Error(value, Reason::Split))
+            .and_then(|(a, b)| {
+                let (a, b) = (EString::from(a), EString::from(b));
+                let a = A::parse_frag(a.clone()).map_err(|_| Error(a, Reason::Parse))?;
+                let b = B::parse_frag(b.clone()).map_err(|_| Error(b, Reason::Parse))?;
+                Ok(Self(a, b))
+            })
     }
 }
 
diff --git a/src/structs/sep_vec.rs b/src/structs/sep_vec.rs
index b48ea7a..ca1ab18 100644
--- a/src/structs/sep_vec.rs
+++ b/src/structs/sep_vec.rs
@@ -1,12 +1,12 @@
 //! Contains the implementations to vec type
 //!
 
-use crate::core::EString;
+use crate::core::{EString, ParseFragment};
 use std::fmt::Write;
 
 /// Wrapper for ``Vec`` to split string by a separator (`SEP`).
 ///
-/// **NOTE**: Required the enabling of the `vec` feature.
+/// **NOTE**: Required the enabling of the `structs` feature.
 ///
 /// # Examples
 ///
@@ -15,7 +15,7 @@ use std::fmt::Write;
 ///
 /// type CommaVec<T> = SepVec<T, ','>;
 ///
-/// fn main() -> Result<(), estring::ParseError> {
+/// fn main() -> estring::Result<()> {
 ///     let res = EString::from("1,2,3").parse::<CommaVec<u8>>()?;
 ///     assert_eq!(*res, vec![1, 2, 3]);
 ///     Ok(())
@@ -56,19 +56,17 @@ where
     }
 }
 
-impl<T, const SEP: char> TryFrom<EString> for SepVec<T, SEP>
+impl<T, const SEP: char> ParseFragment for SepVec<T, SEP>
 where
-    T: TryFrom<EString> + std::fmt::Display,
+    T: ParseFragment,
 {
-    type Error = T::Error;
-
-    fn try_from(value: EString) -> Result<Self, Self::Error> {
+    fn parse_frag(value: EString) -> crate::Result<Self> {
         let inner = value
             .split(SEP)
             .map(str::trim)
             .map(EString::from)
-            .map(T::try_from)
-            .collect::<Result<Vec<_>, _>>()?;
+            .map(T::parse_frag)
+            .collect::<crate::Result<Vec<_>>>()?;
         Ok(Self(inner))
     }
 }
@@ -76,7 +74,7 @@ where
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::ParseError;
+    use crate::{Error, Reason};
 
     const COMMA: char = ',';
     const SEMI: char = ';';
@@ -134,8 +132,9 @@ d,e";
     fn should_throw_parse_vec_error() {
         let estr = EString::from("1,2,3,4,5");
         match estr.parse::<SemiVec<i32>>() {
-            Err(ParseError(orig)) => {
-                assert_eq!(orig, String::from("1,2,3,4,5"));
+            Err(Error(orig, reason)) => {
+                assert_eq!(orig, EString::from("1,2,3,4,5"));
+                assert_eq!(reason, Reason::Parse);
             }
             _ => unreachable!(),
         };
diff --git a/src/structs/trio.rs b/src/structs/trio.rs
index 65aa650..5a8681a 100644
--- a/src/structs/trio.rs
+++ b/src/structs/trio.rs
@@ -1,44 +1,21 @@
 //! Contains the implementations to parse triple-tuple type
 //!
 
-use crate::core::EString;
+use super::Pair;
+use crate::core::{EString, ParseFragment};
 use std::fmt::Write;
 
-/// The error type for operations interacting with parsing tuples. Possibly returned from
-/// ``EString::parse``
-#[derive(Debug)]
-pub enum Error {
-    /// The specified input string is not split.
-    Split,
-
-    /// The specified substring of the split input string is not parsed
-    Parse(u8),
-}
-
-impl std::fmt::Display for Error {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        match self {
-            Error::Split => f.write_str("Cannot split input string"),
-            Error::Parse(n) => write!(f, "Cannot parse {} substring", n),
-        }
-    }
-}
-
-impl std::error::Error for Error {}
-
 /// Wrapper for trio (A, B, C) tuple to split string by separators (`S1` and `S2`).
 ///
-/// **NOTE**: Required the enabling of the `tuple` feature.
+/// **NOTE**: Required the enabling of the `structs` feature.
 ///
 /// # Examples
 ///
 /// ```rust
 /// use estring::{Trio, EString};
 ///
-/// type EqTrio<A, B, C> = Trio<A, '=', B, '=', C>;
-///
-/// fn main() -> Result<(), estring::ParseError> {
-///     let res = EString::from("one=two=free").parse::<EqTrio<&str, &str, &str>>()?;
+/// fn main() -> estring::Result<()> {
+///     let res = EString::from("one+two=free").parse::<Trio<&str, '+', &str, '=', &str>>()?;
 ///     assert_eq!(res, Trio("one", "two", "free"));
 ///     Ok(())
 /// }
@@ -69,22 +46,15 @@ where
     }
 }
 
-impl<A, const S1: char, B, const S2: char, C> TryFrom<EString> for Trio<A, S1, B, S2, C>
+impl<A, const S1: char, B, const S2: char, C> ParseFragment for Trio<A, S1, B, S2, C>
 where
-    A: TryFrom<EString>,
-    B: TryFrom<EString>,
-    C: TryFrom<EString>,
+    A: ParseFragment,
+    B: ParseFragment,
+    C: ParseFragment,
 {
-    type Error = Error;
-
-    fn try_from(value: EString) -> Result<Self, Self::Error> {
-        value.split_once(S1).ok_or(Error::Split).and_then(|(a, b)| {
-            let a = A::try_from(EString::from(a)).map_err(|_| Error::Parse(0))?;
-            b.split_once(S2).ok_or(Error::Split).and_then(|(b, c)| {
-                let b = B::try_from(EString::from(b)).map_err(|_| Error::Parse(1))?;
-                let c = C::try_from(EString::from(c)).map_err(|_| Error::Parse(2))?;
-                Ok(Self(a, b, c))
-            })
+    fn parse_frag(value: EString) -> crate::Result<Self> {
+        Pair::<A, S1, EString>::parse_frag(value).and_then(|Pair(a, rest)| {
+            Pair::<B, S2, C>::parse_frag(rest).map(|Pair(b, c)| Self(a, b, c))
         })
     }
 }
@@ -92,7 +62,6 @@ where
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::structs::SepVec;
 
     #[test]
     fn should_parse_into_trio() {