diff --git a/lib/crontab/cron_expression/ecto_type.ex b/lib/crontab/cron_expression/ecto_type.ex
index a27d865..c9a1661 100644
--- a/lib/crontab/cron_expression/ecto_type.ex
+++ b/lib/crontab/cron_expression/ecto_type.ex
@@ -17,6 +17,16 @@ if match?({:module, Ecto.Type}, Code.ensure_compiled(Ecto.Type)) do
           field :schedule, Crontab.CronExpression.Ecto.Type
         end
 
+    ## Casted Values
+
+    It is recommended to only pass `Crontab.CronExpression` structs to the
+    field.
+
+    The type will automatically cast the string representation to a
+    `Crontab.CronExpression` struct. This will however only work for normal
+    (not extended) expressions since the string representation of extended
+    expressions can't be disambiguated from normal expressions.
+
     """
 
     alias Crontab.CronExpression
@@ -25,21 +35,13 @@ if match?({:module, Ecto.Type}, Code.ensure_compiled(Ecto.Type)) do
 
     @behaviour Ecto.Type
 
-    @type map_expression :: %{
-            extended: boolean,
-            reboot: boolean,
-            second: [CronExpression.value(Calendar.second())],
-            minute: [CronExpression.value(Calendar.minute())],
-            hour: [CronExpression.value(Calendar.second())],
-            day: [CronExpression.value(Calendar.day())],
-            month: [CronExpression.value(Calendar.month())],
-            weekday: [CronExpression.value(Calendar.day_of_week())],
-            year: [CronExpression.value(Calendar.year())]
-          }
-
+    @doc false
+    @impl Ecto.Type
     @spec type :: :map
     def type, do: :map
 
+    @doc false
+    @impl Ecto.Type
     @spec cast(any) :: {:ok, CronExpression.t()} | :error
     def cast(cron_expression = %Crontab.CronExpression{}), do: {:ok, cron_expression}
 
@@ -55,6 +57,8 @@ if match?({:module, Ecto.Type}, Code.ensure_compiled(Ecto.Type)) do
 
     def cast(_), do: :error
 
+    @doc false
+    @impl Ecto.Type
     @spec load(any) :: {:ok, CronExpression.t()} | :error
     def load(%{"extended" => extended, "expression" => expression}) do
       load(%{extended: extended, expression: expression})
@@ -69,15 +73,23 @@ if match?({:module, Ecto.Type}, Code.ensure_compiled(Ecto.Type)) do
 
     def load(_), do: :error
 
+    @doc false
+    @impl Ecto.Type
     @spec dump(any) :: {:ok, CronExpression.t()} | :error
     def dump(cron_expression = %CronExpression{extended: extended}) do
       {:ok, %{extended: extended, expression: Composer.compose(cron_expression)}}
     end
 
+    @doc false
+    @impl Ecto.Type
     def dump(_), do: :error
 
+    @doc false
+    @impl Ecto.Type
     def embed_as(_), do: :dump
 
+    @doc false
+    @impl Ecto.Type
     def equal?(term1, term2), do: term1 == term2
   end
 end