diff --git a/.vscode/settings.json b/.vscode/settings.json
index e6eedf9..3666538 100644
--- a/.vscode/settings.json
+++ b/.vscode/settings.json
@@ -1,3 +1,6 @@
 {
-  "rust-analyzer.linkedProjects": ["./examples/demo/Cargo.toml"]
+  "rust-analyzer.linkedProjects": [
+    "./examples/demo/Cargo.toml",
+    "./hframe-core/Cargo.toml"
+  ]
 }
diff --git a/hframe-core/Cargo.lock b/hframe-core/Cargo.lock
new file mode 100644
index 0000000..14240c0
--- /dev/null
+++ b/hframe-core/Cargo.lock
@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "hframe-core"
+version = "0.1.0"
diff --git a/hframe-core/Cargo.toml b/hframe-core/Cargo.toml
new file mode 100644
index 0000000..c6b3cfd
--- /dev/null
+++ b/hframe-core/Cargo.toml
@@ -0,0 +1,6 @@
+[package]
+name = "hframe-core"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
diff --git a/hframe-core/src/composed_area.rs b/hframe-core/src/composed_area.rs
new file mode 100644
index 0000000..62fa94d
--- /dev/null
+++ b/hframe-core/src/composed_area.rs
@@ -0,0 +1,20 @@
+use crate::{geo::*, id::*};
+
+#[derive(Debug, Clone)]
+pub(crate) struct ComposedHtml {
+    pub(crate) content: String,
+}
+
+#[derive(Debug, Clone)]
+pub(crate) enum ComposedAreaKind {
+    Canvas,
+    Html(ComposedHtml),
+}
+
+#[derive(Debug, Clone)]
+pub(crate) struct ComposedArea {
+    pub(crate) id: Id,
+    pub(crate) size: Size,
+    pub(crate) abs_pos: Pos,
+    pub(crate) kind: ComposedAreaKind,
+}
diff --git a/hframe-core/src/context.rs b/hframe-core/src/context.rs
new file mode 100644
index 0000000..a1703a8
--- /dev/null
+++ b/hframe-core/src/context.rs
@@ -0,0 +1,54 @@
+use crate::{
+    composed_area::ComposedArea, platform::Platform, test_platform::TestPlatform, tree::Node,
+};
+
+struct Context<P: Platform> {
+    tree: Node<ComposedArea>,
+    platform: P,
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{
+        composed_area::{ComposedAreaKind, ComposedHtml},
+        geo::{Pos, Size},
+        id::Id,
+    };
+
+    use super::*;
+
+    #[test]
+    fn it_works() {
+        let ctx = Context {
+            tree: Node::new(ComposedArea {
+                id: Id::from("root"),
+                size: Size::new(100.0, 100.0),
+                abs_pos: Pos::new(0.0, 0.0),
+                kind: ComposedAreaKind::Canvas,
+            })
+            .nest(
+                Node::new(ComposedArea {
+                    id: Id::from("child"),
+                    size: Size::new(50.0, 50.0),
+                    abs_pos: Pos::new(10.0, 10.0),
+                    kind: ComposedAreaKind::Canvas,
+                })
+                .nest(Node::new(ComposedArea {
+                    id: Id::from("grandchild"),
+                    size: Size::new(25.0, 25.0),
+                    abs_pos: Pos::new(5.0, 5.0),
+                    kind: ComposedAreaKind::Html(ComposedHtml {
+                        content: "<div>hello</div>".into(),
+                    }),
+                })),
+            ),
+            platform: TestPlatform {
+                mouse_pos: Pos::new(0.0, 0.0),
+            },
+        };
+
+        ctx.tree
+            .find(|node| node.read(|data| data.value.id == Id::from("grandchild")))
+            .unwrap();
+    }
+}
diff --git a/hframe-core/src/geo.rs b/hframe-core/src/geo.rs
new file mode 100644
index 0000000..70e8664
--- /dev/null
+++ b/hframe-core/src/geo.rs
@@ -0,0 +1,37 @@
+#[derive(Debug, Clone, Copy, PartialEq, Default)]
+pub(crate) struct Pos {
+    pub(crate) x: f64,
+    pub(crate) y: f64,
+}
+
+impl Pos {
+    pub(crate) fn new(x: f64, y: f64) -> Self {
+        Pos { x, y }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Default)]
+pub(crate) struct Size {
+    pub(crate) width: f64,
+    pub(crate) height: f64,
+}
+
+impl Size {
+    pub(crate) fn new(width: f64, height: f64) -> Self {
+        Size { width, height }
+    }
+}
+
+/*
+#[derive(Debug, Clone, Copy, PartialEq, Default)]
+struct Rect {
+    pos: Pos,
+    size: Size,
+}
+
+impl Rect {
+    fn new(pos: Pos, size: Size) -> Self {
+        Rect { pos, size }
+    }
+}
+*/
diff --git a/hframe-core/src/id.rs b/hframe-core/src/id.rs
new file mode 100644
index 0000000..b34165a
--- /dev/null
+++ b/hframe-core/src/id.rs
@@ -0,0 +1,34 @@
+use std::hash::{DefaultHasher, Hash, Hasher};
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub(crate) struct Id(u64);
+
+impl From<u64> for Id {
+    fn from(id: u64) -> Self {
+        Id(id)
+    }
+}
+
+impl From<&str> for Id {
+    fn from(id: &str) -> Self {
+        let mut hasher = DefaultHasher::new();
+        id.hash(&mut hasher);
+        Id(hasher.finish())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn it_works() {
+        let id = Id::from("hello");
+        assert_eq!(id, Id::from("hello"));
+        assert_ne!(id, Id::from("world"));
+
+        let id = Id::from(42);
+        assert_eq!(id, Id::from(42));
+        assert_ne!(id, Id::from(43));
+    }
+}
diff --git a/hframe-core/src/lib.rs b/hframe-core/src/lib.rs
new file mode 100644
index 0000000..4480cd5
--- /dev/null
+++ b/hframe-core/src/lib.rs
@@ -0,0 +1,23 @@
+mod composed_area;
+mod context;
+mod geo;
+mod id;
+mod platform;
+mod test_platform;
+mod tree;
+mod web_platform;
+
+pub fn add(left: usize, right: usize) -> usize {
+    left + right
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn it_works() {
+        let result = add(2, 2);
+        assert_eq!(result, 4);
+    }
+}
diff --git a/hframe-core/src/platform.rs b/hframe-core/src/platform.rs
new file mode 100644
index 0000000..e9a9d84
--- /dev/null
+++ b/hframe-core/src/platform.rs
@@ -0,0 +1,5 @@
+use crate::geo::Pos;
+
+pub(crate) trait Platform {
+    fn mouse_pos(&self) -> Pos;
+}
diff --git a/hframe-core/src/test_platform.rs b/hframe-core/src/test_platform.rs
new file mode 100644
index 0000000..212d192
--- /dev/null
+++ b/hframe-core/src/test_platform.rs
@@ -0,0 +1,11 @@
+use crate::{geo::Pos, platform::Platform};
+
+pub(crate) struct TestPlatform {
+    pub(crate) mouse_pos: Pos,
+}
+
+impl Platform for TestPlatform {
+    fn mouse_pos(&self) -> Pos {
+        self.mouse_pos
+    }
+}
diff --git a/hframe-core/src/tree.rs b/hframe-core/src/tree.rs
new file mode 100644
index 0000000..b876a1a
--- /dev/null
+++ b/hframe-core/src/tree.rs
@@ -0,0 +1,137 @@
+use std::{cell::RefCell, fmt::Debug, rc::Rc};
+
+struct Handle<T>(Rc<RefCell<T>>);
+
+impl<T> Clone for Handle<T> {
+    fn clone(&self) -> Self {
+        Handle(Rc::clone(&self.0))
+    }
+}
+
+impl<T> Handle<T> {
+    fn new(value: T) -> Self {
+        Handle(Rc::new(RefCell::new(value)))
+    }
+
+    fn read<R>(&self, f: impl FnOnce(&T) -> R) -> R {
+        match self.0.try_borrow() {
+            Ok(value) => f(&value),
+            Err(_) => panic!("The handle can't be read because it's being written somewhere else. Hint: Search where a `read_mut` closure is being used."),
+        }
+    }
+
+    fn read_mut<R>(&self, f: impl FnOnce(&mut T) -> R) -> R {
+        match self.0.try_borrow_mut() {
+            Ok(mut value) => f(&mut value),
+            Err(_) => panic!("The handle can't be written because it's being read somewhere else. Hint: Search where a `read` closure is being used."),
+        }
+    }
+}
+
+pub(crate) struct NodeData<T: Debug> {
+    pub(crate) value: T,
+    pub(crate) children: Vec<Node<T>>,
+}
+
+pub(crate) struct Node<T: Debug>(Handle<NodeData<T>>);
+
+impl<T: Debug> Clone for Node<T> {
+    fn clone(&self) -> Self {
+        Node(self.0.clone())
+    }
+}
+
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub(crate) enum Walk {
+    Continue,
+    Stop,
+}
+
+impl<T: Debug> Node<T> {
+    pub(crate) fn new(value: T) -> Self {
+        Node(Handle::new(NodeData {
+            value,
+            children: Vec::new(),
+        }))
+    }
+
+    pub(crate) fn nest(&self, node: Node<T>) -> Node<T> {
+        self.read_mut(|data| data.children.push(node));
+        self.clone()
+    }
+
+    fn walk_impl(&self, f: &mut impl FnMut(Node<T>, usize) -> Walk, depth: usize) -> Walk {
+        if f(self.clone(), depth) == Walk::Stop {
+            return Walk::Stop;
+        }
+
+        self.read(|data| {
+            for child in data.children.iter() {
+                if child.walk_impl(f, depth + 1) == Walk::Stop {
+                    return Walk::Stop;
+                }
+            }
+
+            Walk::Continue
+        })
+    }
+
+    pub(crate) fn walk(&self, mut f: impl FnMut(Node<T>, usize) -> Walk) {
+        self.walk_impl(&mut f, 0);
+    }
+
+    // kepp this private to fully hide the handle
+    fn data(&self) -> Handle<NodeData<T>> {
+        self.0.clone()
+    }
+
+    pub(crate) fn find(&self, predicate: impl Fn(Node<T>) -> bool) -> Option<Node<T>> {
+        let mut found = None;
+
+        self.walk(|node, _| {
+            if predicate(node.clone()) {
+                found = Some(node.clone());
+                Walk::Stop
+            } else {
+                Walk::Continue
+            }
+        });
+
+        found
+    }
+
+    pub(crate) fn read<R>(&self, f: impl FnOnce(&NodeData<T>) -> R) -> R {
+        self.data().read(|data| f(&data))
+    }
+
+    pub(crate) fn read_mut<R>(&self, f: impl FnOnce(&mut NodeData<T>) -> R) -> R {
+        self.data().read_mut(|data| f(data))
+    }
+}
+
+impl Debug for Node<String> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        if f.alternate() {
+            self.walk(|node, depth| {
+                node.read(|data| {
+                    writeln!(f, "{:indent$}{:?}", "", data.value, indent = depth * 2).unwrap();
+                    Walk::Continue
+                })
+            });
+        } else {
+            self.read(|data| {
+                write!(f, "{:?}", data.value).unwrap();
+
+                if !data.children.is_empty() {
+                    write!(f, " {{").unwrap();
+                    for child in data.children.iter() {
+                        write!(f, " {:?}", child).unwrap();
+                    }
+                    write!(f, " }}").unwrap();
+                }
+            });
+        }
+
+        Ok(())
+    }
+}
diff --git a/hframe-core/src/web_platform.rs b/hframe-core/src/web_platform.rs
new file mode 100644
index 0000000..a58b73b
--- /dev/null
+++ b/hframe-core/src/web_platform.rs
@@ -0,0 +1,9 @@
+use crate::platform::Platform;
+
+pub struct WebPlatform;
+
+impl Platform for WebPlatform {
+    fn mouse_pos(&self) -> crate::geo::Pos {
+        crate::geo::Pos::new(0.0, 0.0)
+    }
+}