diff --git a/index.html b/index.html
index d8e434f..56501a7 100644
--- a/index.html
+++ b/index.html
@@ -1229,33 +1229,123 @@
 });
 
 'use strict';
-let decimalBullet = Array.from({ length: 100 }, (a, i) => '' + (i + 1));
-let alphaBullet = Array.from({ length: 26 }, (a, i) => String.fromCharCode('a'.charCodeAt(0) + i));
-
-// prettier-ignore
-let romanBullet = ['i', 'ii', 'iii', 'iv', 'v', 'vi', 'vii', 'viii', 'ix', 'x', 'xi', 'xii', 'xiii', 'xiv', 'xv', 'xvi', 'xvii', 'xviii', 'xix', 'xx', 'xxi', 'xxii', 'xxiii', 'xxiv', 'xxv'];
-// prettier-ignore
-let bullets = [decimalBullet, alphaBullet, romanBullet, decimalBullet, alphaBullet, romanBullet];
-
-function addStepNumberText(ol, parentIndex) {
-  for (let i = 0; i < ol.children.length; ++i) {
-    let child = ol.children[i];
-    let index = parentIndex.concat([i]);
-    let applicable = bullets[Math.min(index.length - 1, 5)];
-    let span = document.createElement('span');
-    span.textContent = (applicable[i] || '?') + '. ';
-    span.style.fontSize = '0';
-    span.setAttribute('aria-hidden', 'true');
-    child.prepend(span);
-    let sublist = child.querySelector('ol');
-    if (sublist != null) {
-      addStepNumberText(sublist, index);
+
+// Manually prefix algorithm step list items with hidden counter representations
+// corresponding with their markers so they get selected and copied with content.
+// We read list-style-type to avoid divergence with the style sheet, but
+// for efficiency assume that all lists at the same nesting depth use the same
+// style (except for those associated with replacement steps).
+// We also precompute some initial items for each supported style type.
+// https://w3c.github.io/csswg-drafts/css-counter-styles/
+
+const lowerLetters = Array.from({ length: 26 }, (_, i) =>
+  String.fromCharCode('a'.charCodeAt(0) + i)
+);
+// Implement the lower-alpha 'alphabetic' algorithm,
+// adjusting for indexing from 0 rather than 1.
+// https://w3c.github.io/csswg-drafts/css-counter-styles/#simple-alphabetic
+// https://w3c.github.io/csswg-drafts/css-counter-styles/#alphabetic-system
+const lowerAlphaTextForIndex = i => {
+  let S = '';
+  for (const N = lowerLetters.length; i >= 0; i--) {
+    S = lowerLetters[i % N] + S;
+    i = Math.floor(i / N);
+  }
+  return S;
+};
+
+const weightedLowerRomanSymbols = Object.entries({
+  m: 1000,
+  cm: 900,
+  d: 500,
+  cd: 400,
+  c: 100,
+  xc: 90,
+  l: 50,
+  xl: 40,
+  x: 10,
+  ix: 9,
+  v: 5,
+  iv: 4,
+  i: 1,
+});
+// Implement the lower-roman 'additive' algorithm,
+// adjusting for indexing from 0 rather than 1.
+// https://w3c.github.io/csswg-drafts/css-counter-styles/#simple-numeric
+// https://w3c.github.io/csswg-drafts/css-counter-styles/#additive-system
+const lowerRomanTextForIndex = i => {
+  let value = i + 1;
+  let S = '';
+  for (const [symbol, weight] of weightedLowerRomanSymbols) {
+    if (!value) break;
+    if (weight > value) continue;
+    const reps = Math.floor(value / weight);
+    S += symbol.repeat(reps);
+    value -= weight * reps;
+  }
+  return S;
+};
+
+// Memoize pure index-to-text functions with an exposed cache for fast retrieval.
+const makeCounter = (pureGetTextForIndex, precomputeCount = 30) => {
+  const cache = Array.from({ length: precomputeCount }, (_, i) => pureGetTextForIndex(i));
+  const getTextForIndex = i => {
+    if (i >= cache.length) cache[i] = pureGetTextForIndex(i);
+    return cache[i];
+  };
+  return { getTextForIndex, cache };
+};
+
+const counterByStyle = {
+  __proto__: null,
+  decimal: makeCounter(i => String(i + 1)),
+  'lower-alpha': makeCounter(lowerAlphaTextForIndex),
+  'upper-alpha': makeCounter(i => lowerAlphaTextForIndex(i).toUpperCase()),
+  'lower-roman': makeCounter(lowerRomanTextForIndex),
+  'upper-roman': makeCounter(i => lowerRomanTextForIndex(i).toUpperCase()),
+};
+const fallbackCounter = makeCounter(() => '?');
+const counterByDepth = [];
+
+function addStepNumberText(
+  ol,
+  depth = 0,
+  special = [...ol.classList].some(c => c.startsWith('nested-'))
+) {
+  let counter = !special && counterByDepth[depth];
+  if (!counter) {
+    const counterStyle = getComputedStyle(ol)['list-style-type'];
+    counter = counterByStyle[counterStyle];
+    if (!counter) {
+      console.warn('unsupported list-style-type', {
+        ol,
+        counterStyle,
+        id: ol.closest('[id]')?.getAttribute('id'),
+      });
+      counterByStyle[counterStyle] = fallbackCounter;
+      counter = fallbackCounter;
+    }
+    if (!special) {
+      counterByDepth[depth] = counter;
+    }
+  }
+  const { cache, getTextForIndex } = counter;
+  let i = (Number(ol.getAttribute('start')) || 1) - 1;
+  for (const li of ol.children) {
+    const marker = document.createElement('span');
+    marker.textContent = `${i < cache.length ? cache[i] : getTextForIndex(i)}. `;
+    marker.setAttribute('aria-hidden', 'true');
+    li.prepend(marker);
+    for (const sublist of li.querySelectorAll(':scope > ol')) {
+      addStepNumberText(sublist, depth + 1, special);
     }
+    i++;
   }
 }
+
 document.addEventListener('DOMContentLoaded', () => {
   document.querySelectorAll('emu-alg > ol').forEach(ol => {
-    addStepNumberText(ol, []);
+    addStepNumberText(ol);
   });
 });
 
@@ -1450,6 +1540,10 @@
   list-style-type: lower-roman;
 }
 
+emu-alg [aria-hidden=true] {
+  font-size: 0;
+}
+
 emu-eqn {
   display: block;
   margin-left: 4em;
@@ -1501,7 +1595,7 @@
   margin-bottom: 0;
 }
 
-emu-table td code {
+emu-table:not(.code) td code {
   white-space: normal;
 }
 
@@ -2525,7 +2619,7 @@
 </ul></div><div id="menu-toggle"><svg xmlns="http://www.w3.org/2000/svg" style="width:100%; height:100%; stroke:currentColor" viewBox="0 0 120 120">
       <title>Menu</title>
       <path stroke-width="10" stroke-linecap="round" d="M30,60 h60  M30,30 m0,5 h60  M30,90 m0,-5 h60"></path>
-    </svg></div><div id="menu-spacer" class="menu-spacer"></div><div id="menu"><div id="menu-search"><input type="text" id="menu-search-box" placeholder="Search..."><div id="menu-search-results" class="inactive"></div></div><div id="menu-pins"><div class="menu-pane-header">Pins</div><ul id="menu-pins-list"></ul></div><div class="menu-pane-header">Table of Contents</div><div id="menu-toc"><ol class="toc"><li><span class="item-toggle-none"></span><a href="#sec-demo-clause" title="This is an emu-clause"><span class="secnum">1</span> This is an emu-clause</a></li><li><span class="item-toggle-none"></span><a href="#sec-copyright-and-software-license" title="Copyright &amp; Software License"><span class="secnum">A</span> Copyright &amp; Software License</a></li></ol></div></div><div id="spec-container"><h1 class="version">Stage -1 Draft / November 28, 2022</h1><h1 class="title">AssertionError Proposal</h1>
+    </svg></div><div id="menu-spacer" class="menu-spacer"></div><div id="menu"><div id="menu-search"><input type="text" id="menu-search-box" placeholder="Search..."><div id="menu-search-results" class="inactive"></div></div><div id="menu-pins"><div class="menu-pane-header">Pins</div><ul id="menu-pins-list"></ul></div><div class="menu-pane-header">Table of Contents</div><div id="menu-toc"><ol class="toc"><li><span class="item-toggle-none"></span><a href="#sec-demo-clause" title="This is an emu-clause"><span class="secnum">1</span> This is an emu-clause</a></li><li><span class="item-toggle-none"></span><a href="#sec-copyright-and-software-license" title="Copyright &amp; Software License"><span class="secnum">A</span> Copyright &amp; Software License</a></li></ol></div></div><div id="spec-container"><h1 class="version">Stage -1 Draft / January 25, 2023</h1><h1 class="title">AssertionError Proposal</h1>
 
 <emu-clause id="sec-demo-clause">
   <h1><span class="secnum">1</span> This is an emu-clause</h1>
@@ -2535,7 +2629,7 @@ <h1><span class="secnum">1</span> This is an emu-clause</h1>
       <h1><span class="secnum">A</span> Copyright &amp; Software License</h1>
       
       <h2>Copyright Notice</h2>
-      <p>© 2022 The TC39 AssertionError Proposal Authors</p>
+      <p>© 2023 The TC39 AssertionError Proposal Authors</p>
 
       <h2>Software License</h2>
       <p>All Software contained in this document ("Software") is protected by copyright and is being made available under the "BSD License", included below. This Software may be subject to third party rights (rights from parties other than Ecma International), including patent rights, and no licenses under such third party rights are granted under this license even if the third party concerned is a member of Ecma International. SEE THE ECMA CODE OF CONDUCT IN PATENT MATTERS AVAILABLE AT https://ecma-international.org/memento/codeofconduct.htm FOR INFORMATION REGARDING THE LICENSING OF PATENT CLAIMS THAT ARE REQUIRED TO IMPLEMENT ECMA INTERNATIONAL STANDARDS.</p>
diff --git a/package.json b/package.json
index bdb44fa..7708281 100644
--- a/package.json
+++ b/package.json
@@ -10,6 +10,6 @@
   "repository": "github:DerekNonGeneric/proposal-assertion-error",
   "license": "MIT",
   "devDependencies": {
-    "ecmarkup": "16.0.0"
+    "ecmarkup": "16.0.1"
   }
 }