Make clear why this method can fail

Signed-off-by: Matthias Beyer <mail@beyermatthias.de>

1 files changed, 3 insertions, 2 deletions

diff --git a/src/builder.rs b/src/builder.rs
index c1318be..23090c6 100644
--- a/src/builder.rs
+++ b/src/builder.rs
@@ -75,7 +75,8 @@ impl ConfigBuilder {
     /// This value can be overwritten by any [`Source`] or override.
     ///
     /// # Errors
-    /// Method can fail if `key` is not valid.
+    ///
+    /// Fails if `Expression::from_str(key)` fails.
     pub fn set_default<T>(&mut self, key: &str, value: T) -> error::Result<&mut ConfigBuilder>
     where
         T: Into<Value>,
@@ -101,7 +102,7 @@ impl ConfigBuilder {
     ///
     /// # Errors
     ///
-    /// Method can fail if `key` is not valid.
+    /// Fails if `Expression::from_str(key)` fails.
     pub fn set_override<T>(&mut self, key: &str, value: T) -> error::Result<&mut ConfigBuilder>
     where
         T: Into<Value>,