Add case alternatives for switch.

src/tokenizer.rs

@@ -283,7 +283,7 @@ impl AddAssign for Position {
 
 /// _(internals)_ A span consisting of a starting and an ending [positions][Position].
 /// Exported under the `internals` feature only.
-#[derive(Eq, PartialEq, Ord, PartialOrd, Hash, Clone, Copy, Default)]
+#[derive(Eq, PartialEq, Ord, PartialOrd, Hash, Clone, Copy)]
 pub struct Span {
     /// Starting [position][Position].
     start: Position,
@@ -291,6 +291,12 @@ pub struct Span {
     end: Position,
 }
 
+impl Default for Span {
+    fn default() -> Self {
+        Self::NONE
+    }
+}
+
 impl Span {
     /// Empty [`Span`].
     pub const NONE: Self = Self::new(Position::NONE, Position::NONE);