Document what feature everything requires
diff --git a/src/spanned.rs b/src/spanned.rs
index 2da45d7..c844fc7 100644
--- a/src/spanned.rs
+++ b/src/spanned.rs
@@ -9,6 +9,9 @@
//! A trait that can provide the `Span` of the complete contents of a syntax
//! tree node.
//!
+//! *This module is available if Syn is built with both the `"parsing"` and
+//! `"printing"` features.*
+//!
//! # Example
//!
//! Suppose in a procedural macro we have a [`Type`] that we want to assert
@@ -97,6 +100,9 @@
/// See the [module documentation] for an example.
///
/// [module documentation]: index.html
+///
+/// *This trait is available if Syn is built with both the `"parsing"` and
+/// `"printing"` features.*
pub trait Spanned {
/// Returns a `Span` covering the complete contents of this syntax tree
/// node, or [`Span::call_site()`] if this node is empty.