diff --git a/documentation/writing-installers.md b/documentation/writing-installers.md
new file mode 100644
index 0000000..63c2e6f
--- /dev/null
+++ b/documentation/writing-installers.md
@@ -0,0 +1,100 @@
+# Writing Installers
+
+Generate the install task:
+```
+mix igniter.gen.task my_dep.install
+```
+All of the work will be done in the igniter call:
+
+```elixir
+@impl Igniter.Mix.Task
+def igniter(igniter) do
+  # Do your work here and return an updated igniter
+  igniter
+  |> Igniter.add_warning("mix routex.install is not yet implemented")
+end
+```
+
+## Fetching Dependency
+
+```elixir
+if Igniter.Project.Deps.has_dep?(igniter, :my_dep) do
+  igniter
+else
+  igniter
+  |> Igniter.Project.Deps.add_dep({:my_dep, "~> 1.0"})
+  |> Igniter.apply_and_fetch_dependencies(error_on_abort?: true, yes_to_deps: true)
+end
+```
+
+Check does the dependency already exist and if not add it and apply it.
+
+
+## Creating a module
+
+```elixir
+Igniter.Project.Module.create_module(igniter, module, """
+use MyDep.Module
+""")
+```
+
+Create a new module that uses some module from your application.
+
+## Modifying a module
+
+For example:
+
+```elixir
+defmodule SomeModule do
+  alias Some.Example
+
+  def some_function(a, b) do
+    Example.function(a, b)
+  end
+end
+```
+
+Find that module and update it:
+
+```elixir
+Igniter.Project.Module.find_and_update_module!(igniter, SomeModule, fn zipper ->
+  {:ok, igniter}
+end)
+```
+
+In the function block use [`within/2`](https://hexdocs.pm/igniter/Igniter.Code.Common.html#within/2) to do multiple modifications. Find the part you want to change and modify it.
+
+For example:
+ - replace alias with an import:
+```elixir
+Igniter.Code.Common.within(fn zipper ->
+  pred = &match?(%Zipper{node: {:alias, _, _}}, &1)
+  zipper = Common.remove(zipper, pred)
+  line = "import Some.Example, only: [:function]"
+  {:ok, Common.add_code(zipper, line, placement: :before)}
+end)
+```
+
+ - replace function block:
+ ```elixir
+Igniter.Code.Common.within(fn zipper ->
+  {:ok, zipper} = move_to_function(zipper, :some_function)
+  {:ok, zipper} = Common.move_to_do_block(zipper)
+  line = "my_private_function!(function(a, b))"
+  {:ok, Igniter.Code.Common.replace_code(zipper, line)}
+end)
+```
+
+ - add a block:
+ ```elixir
+Igniter.Code.Common.within(fn zipper ->
+  block = """
+  defp private_function!({:ok, result}), do: result
+  defp private_function!(_), do: raise "Something went wrong!"
+  """
+
+  {:ok, Common.add_code(zipper, block, placement: :after)}
+end)
+```
+
+You can chain within blocks using `with`.
\ No newline at end of file
diff --git a/mix.exs b/mix.exs
index 4a0a50c..7c783ac 100644
--- a/mix.exs
+++ b/mix.exs
@@ -53,6 +53,7 @@ defmodule Igniter.MixProject do
       extras: [
         {"README.md", title: "Home"},
         "documentation/writing-generators.md",
+        "documentation/writing-installers.md",
         "documentation/configuring-igniter.md",
         "documentation/upgrades.md",
         "CHANGELOG.md"
diff --git a/test/igniter/code/within_test.exs b/test/igniter/code/within_test.exs
new file mode 100644
index 0000000..99bf4a6
--- /dev/null
+++ b/test/igniter/code/within_test.exs
@@ -0,0 +1,82 @@
+defmodule Igniter.Code.WithinTest do
+  alias Igniter.Code.Common
+  alias Sourceror.Zipper
+  use ExUnit.Case
+  import Igniter.Test
+
+  describe "with within" do
+    test "performs multiple changes to some module" do
+      test_project()
+      |> Igniter.create_new_file("lib/some_module.ex", """
+      defmodule SomeModule do
+        alias Some.Example
+
+        def some_function(a, b) do
+          Example.function(a, b)
+        end
+      end
+      """)
+      |> apply_igniter!()
+      |> Igniter.Project.Module.find_and_update_module!(SomeModule, fn zipper ->
+        zipper
+        |> within!(fn zipper ->
+          pred = &match?(%Zipper{node: {:alias, _, _}}, &1)
+          zipper = Common.remove(zipper, pred)
+          line = "import Some.Example, only: [:function]"
+          {:ok, Common.add_code(zipper, line, placement: :before)}
+        end)
+        |> within!(fn zipper ->
+          {:ok, zipper} = move_to_function(zipper, :some_function)
+          {:ok, zipper} = Common.move_to_do_block(zipper)
+          line = "my_private_function!(function(a, b))"
+          {:ok, Igniter.Code.Common.replace_code(zipper, line)}
+        end)
+        |> within!(fn zipper ->
+          block = """
+          defp private_function!({:ok, result}), do: result
+          defp private_function!(_), do: raise "Something went wrong!"
+          """
+
+          {:ok, Common.add_code(zipper, block, placement: :after)}
+        end)
+        |> then(fn zipper -> {:ok, zipper} end)
+      end)
+      |> Igniter.Refactors.Rename.rename_function(
+        {SomeModule, :some_function},
+        {SomeModule, :some_function!},
+        arity: 2
+      )
+      |> assert_has_patch("lib/some_module.ex", """
+          |defmodule SomeModule do
+        - |  alias Some.Example
+        + |  import Some.Example, only: [:function]
+          |
+        - |  def some_function(a, b) do
+        - |    Example.function(a, b)
+        + |  def some_function!(a, b) do
+        + |    my_private_function!(function(a, b))
+          |  end
+        + |
+        + |  defp private_function!({:ok, result}),
+        + |    do: result
+        + |
+        + |  defp private_function!(_),
+        + |    do: raise("Something went wrong!")
+          |end
+      """)
+    end
+  end
+
+  defp within!(zipper, function) do
+    case Common.within(zipper, function) do
+      {:ok, zipper} -> zipper
+      :error -> raise "Error calling within"
+    end
+  end
+
+  defp move_to_function(zipper, function) do
+    Igniter.Code.Common.move_to(zipper, fn zipper ->
+      Igniter.Code.Function.function_call?(zipper, function)
+    end)
+  end
+end