diff --git a/src/lib.rs b/src/lib.rs
index 5b69801..9e77169 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -118,9 +118,18 @@ pub trait GraphLike<Node, NodeId> {
 }
 
 pub trait Ruleset<Node, NodeId> {
+    /// Calculate the "entropy" of a node, based on the current state of the graph. Should return
+    /// None if the node is impossible, and Some(entropy) if it is possible. The exact meaning of
+    /// entropy is up to the implementation, but it should be a value that can be compared between
+    /// nodes to determine which one is more "constrained". For example, it could be the number of
+    /// possible values that the node can take, or the number of empty neighbours it has.
+    ///
+    /// By default the WFC algorithm chooses the node with the lowest entropy to "collapse"
     fn entropy(&self, graph: &impl GraphLike<Node, NodeId>, id: NodeId) -> Option<f32>
     where
         NodeId: Copy;
+    /// Choose a node to "collapse" to, based on the current state of the graph. Should return None
+    /// if the node is impossible.
     fn choose(
         &self,
         graph: &impl GraphLike<Node, NodeId>,