Document what feature everything requires
diff --git a/src/error.rs b/src/error.rs
index 2abfbc4..23d2a1a 100644
--- a/src/error.rs
+++ b/src/error.rs
@@ -15,6 +15,8 @@
/// Refer to the [module documentation] for details about parsing in Syn.
///
/// [module documentation]: index.html
+///
+/// *This type is available if Syn is built with the `"parsing"` feature.*
pub type PResult<'a, O> = Result<(O, Cursor<'a>), ParseError>;
/// An error with a default error message.
@@ -29,6 +31,8 @@
/// Refer to the [module documentation] for details about parsing in Syn.
///
/// [module documentation]: index.html
+///
+/// *This type is available if Syn is built with the `"parsing"` feature.*
#[derive(Debug)]
pub struct ParseError(Option<String>);