Improve value casting infrastructure

1 files changed, 16 insertions, 0 deletions

diff --git a/src/model/label.rs b/src/model/label.rs
new file mode 100644
index 00000000..ef8f3edd
--- /dev/null
+++ b/src/model/label.rs
@@ -0,0 +1,16 @@
+use std::fmt::{self, Debug, Formatter};
+
+use ecow::EcoString;
+
+/// A label for an element.
+#[derive(Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
+pub struct Label(pub EcoString);
+
+impl Debug for Label {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        write!(f, "<{}>", self.0)
+    }
+}
+
+/// Indicates that an element cannot be labelled.
+pub trait Unlabellable {}