diff --git a/src/file.rs b/src/file.rs
index d61ee48..7cae620 100644
--- a/src/file.rs
+++ b/src/file.rs
@@ -6,7 +6,8 @@ use crate::{Error, Partial, error::ErrorInner};
 /// A file as source for configuration.
 ///
 /// By default, the file is considered optional, meaning that on [`File::load`],
-/// if the file does not exist, `Partial::empty()` is returned.
+/// if the file does not exist, [`Partial::empty()`][crate::Partial::empty] is
+/// returned.
 pub struct File {
     path: PathBuf,
     format: FileFormat,
diff --git a/src/lib.rs b/src/lib.rs
index 5b43abe..a3cc35a 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -108,7 +108,8 @@ pub use self::{
 ///
 /// - **`Option<T>`**: this marks the field as an optional field. All other
 ///   fields are non-optional and will raise an error if while loading the
-///   configuration, no value has been set for them.
+///   configuration, no value has been set for them. Optional fields cannot have
+///   a `#[config(default = ...)]` attribute as that would not make sense.
 ///
 ///
 ///
diff --git a/src/meta.rs b/src/meta.rs
index 82f3463..954ad80 100644
--- a/src/meta.rs
+++ b/src/meta.rs
@@ -7,6 +7,7 @@ use core::fmt;
 // fine, but before reaching 1.0 I need to figure out how to allow future
 // additions without breaking stuff.
 
+/// Root type.
 #[derive(Clone, Copy, Debug)]
 pub struct Meta {
     /// The type (struct) name.
@@ -38,9 +39,11 @@ pub enum FieldKind {
 
 #[derive(Clone, Copy, Debug)]
 pub enum LeafKind {
+    /// A leaf field with a non `Option<_>` type.
     Required {
         default: Option<Expr>,
     },
+    /// A leaf field with an `Option<_>` type.
     Optional,
 }
 
diff --git a/src/yaml.rs b/src/yaml.rs
index 9c7885d..fde9af4 100644
--- a/src/yaml.rs
+++ b/src/yaml.rs
@@ -1,3 +1,6 @@
+//! YAML specific features. This module only exists if the Cargo feature `yaml`
+//! is enabled.
+
 use std::fmt::{self, Write};
 
 use crate::{