diff --git a/book/en/src/by-example/app.md b/book/en/src/by-example/app.md
index c84f7a41c9..e8e1d7a62e 100644
--- a/book/en/src/by-example/app.md
+++ b/book/en/src/by-example/app.md
@@ -6,6 +6,32 @@ This is the smallest possible RTIC application:
 {{#include ../../../../examples/smallest.rs}}
 ```
 
+All RTIC applications use the [`app`] attribute (`#[app(..)]`). This attribute
+must be applied to a `mod`-item. The `app` attribute has a mandatory `device`
+argument that takes a *path* as a value. This must be a full path pointing to a
+*peripheral access crate* (PAC) generated using [`svd2rust`] **v0.14.x** or
+newer. More details can be found in the [Starting a new project](./new.md)
+section.
+
+The `app` attribute will expand into a suitable entry point so it's not required
+to use the [`cortex_m_rt::entry`] attribute.
+
+[`app`]: ../../../api/cortex_m_rtic_macros/attr.app.html
+[`svd2rust`]: https://crates.io/crates/svd2rust
+[`cortex_m_rt::entry`]: ../../../api/cortex_m_rt_macros/attr.entry.html
+
+## `init`
+
+Within the `app` module the attribute expects to find an initialization
+function marked with the `init` attribute. This function must have
+signature `fn(init::Context) -> (init::LateResources, init::Monotonics)`.
+
+This initialization function will be the first part of the application to run.
+The `init` function will run *with interrupts disabled* and has exclusive access
+to Cortex-M where the `bare_metal::CriticalSection` token is available as `cs`.
+And optionally, device specific peripherals through the `core` and `device` fields
+of `init::Context`.
+
 `static mut` variables declared at the beginning of `init` will be transformed
 into `&'static mut` references that are safe to access. Notice, this feature may be deprecated in next release, see `task_local` resources.
 
@@ -31,7 +57,6 @@ $ cargo run --example init
 > triple to cargo (e.g `cargo run --example init --target thumbv7m-none-eabi`) or
 > configure a device to be used by default when building the examples in `.cargo/config.toml`.
 > In this case, we use a Cortex M3 emulated in QEMU so the target is `thumbv7m-none-eabi`.
-> See [`Starting a new project`](./new.md) for more info.
 
 ## `idle`