diff --git a/deno.json b/deno.json
index 2fc4811..cc57bbd 100644
--- a/deno.json
+++ b/deno.json
@@ -8,6 +8,6 @@
     "mock": "https://deno.land/std@0.196.0/testing/mock.ts"
   },
   "compilerOptions": {
-    "lib": ["deno.ns", "dom"]
+    "lib": ["deno.ns", "dom", "dom.iterable"]
   }
 }
diff --git a/public/common/allChildrenOf.js b/public/common/allChildrenOf.js
new file mode 100644
index 0000000..edfee1d
--- /dev/null
+++ b/public/common/allChildrenOf.js
@@ -0,0 +1,12 @@
+// @ts-check
+
+/**
+ * @param {HTMLElement} element
+ * @returns {Generator<HTMLElement, void, unknown>}
+ */
+export default function* allChildrenOf(element) {
+  yield element;
+  for (const child of element.children ?? []) {
+    yield* allChildrenOf(/** @type {HTMLElement} */ (child));
+  }
+}
diff --git a/public/png/explorer.js b/public/png/explorer.js
index 52ac1ef..d72d590 100644
--- a/public/png/explorer.js
+++ b/public/png/explorer.js
@@ -2,6 +2,8 @@
 
 import crel, { fragment } from "../common/crel.js";
 import formatBytes from "../common/formatBytes.js";
+import allChildrenOf from "../common/allChildrenOf.js";
+import * as nodePath from "./nodePath.js";
 /** @typedef {import("./nodePath.js").NodePath} NodePath */
 /** @typedef {import("../../types/png.d.ts").PngNode} PngNode */
 
@@ -11,6 +13,12 @@ import formatBytes from "../common/formatBytes.js";
  * @returns {NodeUi}
  */
 
+/**
+ * @typedef {object} HoveringOver
+ * @prop {"bytes" | "tree"} side
+ * @prop {NodePath} path
+ */
+
 /**
  * @param {PngNode} rootNode
  * @param {NodeUiFn} getNodeUi
@@ -22,6 +30,142 @@ export default (rootNode, getNodeUi) => {
   const outerBytesEl = crel("div", { class: "bytes" }, bytesRootEl);
   const outerTreeEl = crel("div", { class: "tree" }, treeRootEl);
 
+  /** @type {null | HoveringOver} */
+  let hoveringOver = null;
+
+  const rerender = () => {
+    // TODO: Remove this console.log
+    console.log("rerendering", JSON.stringify(hoveringOver));
+
+    /**
+     * @callback IsActivatedFn
+     * @param {NodePath} path
+     * @returns {boolean}
+     */
+    /** @type {IsActivatedFn} */ let isByteElActivated;
+    /** @type {IsActivatedFn} */ let isTreeElActivated;
+    if (hoveringOver) {
+      const hoveredPath = hoveringOver.path;
+      switch (hoveringOver.side) {
+        case "bytes":
+          isByteElActivated = (path) => nodePath.isEqualTo(path, hoveredPath);
+          isTreeElActivated = (path) =>
+            nodePath.isSupersetOf(path, hoveredPath);
+          break;
+        case "tree":
+          isByteElActivated = (path) =>
+            nodePath.isSupersetOf(hoveredPath, path);
+          isTreeElActivated = (path) => nodePath.isEqualTo(path, hoveredPath);
+          break;
+        default:
+          throw new Error("Unexpected hovering over");
+      }
+    } else {
+      isByteElActivated = isTreeElActivated = () => false;
+    }
+
+    for (const bytesEl of allChildrenOf(bytesRootEl)) {
+      const path = elPath(bytesEl);
+      if (path) {
+        bytesEl.classList.toggle("activated", isByteElActivated(path));
+      } else {
+        throw new Error("Expected a path");
+      }
+    }
+    for (const treeEl of allChildrenOf(treeRootEl)) {
+      const path = elPath(treeEl);
+      if (!path) continue;
+      treeEl.classList.toggle("activated", isTreeElActivated(path));
+    }
+  };
+
+  outerBytesEl.addEventListener("click", (event) => {
+    if (!(event.target instanceof HTMLElement)) return;
+
+    const rawPath = event.target?.dataset?.path;
+    if (!rawPath) return;
+
+    for (const explorerEl of allChildrenOf(outerTreeEl)) {
+      if (explorerEl.dataset.path) explorerEl.removeAttribute("open");
+    }
+
+    const leafEl = outerTreeEl.querySelector(
+      `details[data-path="${rawPath}"]`,
+    );
+    let currentTreeEl = leafEl;
+    while (currentTreeEl && (currentTreeEl !== outerTreeEl)) {
+      currentTreeEl.setAttribute("open", "open");
+      currentTreeEl = currentTreeEl.parentElement;
+    }
+    leafEl?.scrollIntoView({ behavior: "smooth" });
+  });
+
+  outerBytesEl.addEventListener("mousemove", (event) => {
+    if (!(event.target instanceof HTMLElement)) return;
+    const path = elPath(event.target);
+    if (!path) return;
+
+    hoveringOver = { side: "bytes", path };
+    rerender();
+  });
+
+  outerBytesEl.addEventListener("mouseout", (event) => {
+    if (event.target !== outerBytesEl) return;
+
+    if (hoveringOver?.side === "bytes") {
+      hoveringOver = null;
+      rerender();
+    }
+  });
+
+  /** @param {UIEvent} event */
+  const onFocusExplorerTree = (event) => {
+    if (!(event.target instanceof HTMLElement)) return;
+
+    // We don't update the state in these situations to avoid UI jitter.
+    if (event.target.classList.contains("children")) return;
+
+    /** @type {null | HTMLElement} */ let nodeToCheckForPath = event.target;
+    while (nodeToCheckForPath && (nodeToCheckForPath !== outerTreeEl)) {
+      if (nodeToCheckForPath.dataset.path) break;
+      nodeToCheckForPath = nodeToCheckForPath.parentElement;
+    }
+    const path = nodeToCheckForPath && elPath(nodeToCheckForPath);
+    if (!path) return;
+
+    hoveringOver = { side: "tree", path };
+    rerender();
+  };
+  /** @param {UIEvent} event */
+  const onBlurExplorerTree = (event) => {
+    if (
+      (event.target !== outerTreeEl) &&
+      (event.target !== outerTreeEl.children[0]) &&
+      (hoveringOver?.side !== "tree")
+    ) return;
+    hoveringOver = null;
+    rerender();
+  };
+  outerTreeEl.addEventListener("mousemove", onFocusExplorerTree);
+  outerTreeEl.addEventListener("focusin", onFocusExplorerTree);
+  outerTreeEl.addEventListener("mouseout", onBlurExplorerTree);
+  outerTreeEl.addEventListener("focusout", onBlurExplorerTree);
+
+  outerTreeEl.addEventListener("click", (event) => {
+    if (!(event.target instanceof HTMLElement)) return;
+
+    /** @type {null | HTMLElement} */ let nodeToCheckForPath = event.target;
+    while (nodeToCheckForPath && (nodeToCheckForPath !== outerTreeEl)) {
+      if (nodeToCheckForPath.dataset.path) break;
+      nodeToCheckForPath = nodeToCheckForPath.parentElement;
+    }
+    const rawPath = nodeToCheckForPath?.dataset.path;
+    if (!rawPath) return;
+
+    const bytesEl = outerBytesEl.querySelector(`[data-path="${rawPath}"]`);
+    bytesEl?.scrollIntoView({ behavior: "smooth" });
+  });
+
   return fragment(outerBytesEl, outerTreeEl);
 };
 
@@ -71,3 +215,9 @@ const traverse = (node, path, getNodeUi) => {
 
   return [nodeBytesEl, nodeTreeEl];
 };
+
+/**
+ * @param {HTMLElement} el
+ * @returns {null | NodePath}
+ */
+const elPath = (el) => nodePath.parse(el.dataset?.path);
diff --git a/public/png/nodePath.js b/public/png/nodePath.js
index 54fdbd6..092cf9c 100644
--- a/public/png/nodePath.js
+++ b/public/png/nodePath.js
@@ -26,5 +26,29 @@
  */
 export const parse = (value) => {
   if (typeof value !== "string") return null;
-  return value.split(".").map(Number);
+  if (!value) return [];
+  return value.split(",").map((str) => {
+    const result = parseInt(str, 10);
+    if (Number.isFinite(result)) return result;
+    throw new Error(`Invalid node path: ${value}`);
+  });
+};
+
+/**
+ * @param {NodePath} a
+ * @param {NodePath} b
+ * @returns {boolean}
+ */
+export const isEqualTo = (a, b) => a.length === b.length && isSupersetOf(a, b);
+
+/**
+ * @param {NodePath} smaller
+ * @param {NodePath} bigger
+ * @returns {boolean}
+ */
+export const isSupersetOf = (smaller, bigger) => {
+  for (let i = 0; i < smaller.length; i++) {
+    if (smaller[i] !== bigger[i]) return false;
+  }
+  return true;
 };
diff --git a/test/png/nodePath.test.ts b/test/png/nodePath.test.ts
new file mode 100644
index 0000000..06ec4fb
--- /dev/null
+++ b/test/png/nodePath.test.ts
@@ -0,0 +1,20 @@
+import { assert, assertEquals } from "assert";
+import { isEqualTo, isSupersetOf, parse } from "../../public/png/nodePath.js";
+
+Deno.test("parse", () => {
+  assertEquals(parse(""), []);
+  assertEquals(parse("1"), [1]);
+  assertEquals(parse("1,2,3"), [1, 2, 3]);
+});
+
+Deno.test("isEqualTo", () => {
+  assert(isEqualTo([], []));
+  assert(isEqualTo([1, 2, 3], [1, 2, 3]));
+  assert(!isEqualTo([1, 2], [1, 2, 3]));
+});
+
+Deno.test("isSupersetOf", () => {
+  assert(isSupersetOf([1, 2, 3], [1, 2, 3]));
+  assert(isSupersetOf([1, 2], [1, 2, 3]));
+  assert(!isSupersetOf([1, 2, 3], [1, 2]));
+});