lyngweb: introduce reusable editor and highlighting utilities

lyngweb/README.md

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+### Lyng Web utilities (`:lyngweb`)
+
+Reusable JS/Compose for Web utilities and UI pieces for Lyng-powered sites. The module is self-sufficient: adding it as a dependency is enough — no external CSS classes are required for its editor overlay to render correctly.
+
+#### What’s inside
+
+- `EditorWithOverlay` — a pure code editor Composable with a syntax-highlight overlay. It keeps a native `<textarea>` for input/caret while rendering highlighted HTML on top, staying in perfect glyph alignment. No built-in buttons or actions.
+- HTML utilities for Markdown pipelines:
+  - `ensureBootstrapCodeBlocks(html: String): String` — adds `class="code"` to `<pre>` blocks (for Bootstrap-like styling).
+  - `highlightLyngHtml(html: String): String` — transforms Lyng code blocks inside HTML into highlighted spans using `hl-*` classes.
+  - `htmlEscape(s: String): String` — HTML-escape utility used by the highlighter.
+- Backward-compatible `net.sergeych.site.SiteHighlight.renderHtml(text)` that renders a highlighted string with the same `hl-*` classes used by the site.
+
+All essential styles for the editor are injected inline; there is no dependency on external CSS class names (e.g., `editor-overlay`). You can still override visuals with your own CSS if desired.
+
+---
+
+#### Quick start
+
+1) Add the dependency in your JS `build.gradle.kts`:
+
+```kotlin
+dependencies {
+    implementation(project(":lyngweb"))
+}
+```
+
+2) Use the editor in a Compose HTML page:
+
+```kotlin
+@Composable
+fun TryLyngSnippet() {
+    var code by remember { mutableStateOf("""
+        // Type Lyng code here
+        import lyng.stdlib
+        [1,2,3].map { it * 10 }
+    """.trimIndent()) }
+
+    fun runCode() { /* evaluate code in your Scope */ }
+
+    Div({ classes("mb-3") }) {
+        Div({ classes("form-label") }) { Text("Code") }
+        EditorWithOverlay(
+            code = code,
+            setCode = { code = it },
+            // Optionally handle keyboard shortcuts (e.g., Ctrl/Cmd+Enter to run):
+            onKeyDown = { ev ->
+                val ctrlOrMeta = ev.ctrlKey || ev.metaKey
+                if (ctrlOrMeta && ev.key.lowercase() == "enter") {
+                    ev.preventDefault()
+                    runCode()
+                }
+            }
+        )
+    }
+
+    // Your own action buttons
+    // ...your own action buttons...
+}
+```
+
+The editor provides:
+- Tab insertion with configurable `tabSize` (default 4)
+- Smart newline indentation (copies the leading spaces of the current line)
+- Scroll sync and 1:1 glyph alignment between overlay and textarea
+- Inline styles for overlay/textarea; no external CSS required
+
+---
+
+#### Highlight Lyng code inside Markdown HTML
+
+If you render Markdown to HTML first (e.g., with `marked`), you can post-process it with `lyngweb` to highlight Lyng code blocks:
+
+```kotlin
+fun renderMarkdownLyng(mdHtml: String): String {
+    // 1) ensure <pre> blocks have class="code"
+    val withPre = ensureBootstrapCodeBlocks(mdHtml)
+    // 2) highlight <code class="language-lyng"> blocks
+    return highlightLyngHtml(withPre)
+}
+```
+
+Lyng tokens are wrapped into spans with classes like `hl-kw`, `hl-id`, `hl-num`, `hl-cmt`, etc. You can style them as you wish, for example:
+
+```css
+.hl-kw { color: #6f42c1; font-weight: 600; }
+.hl-id { color: #1f2328; }
+.hl-num { color: #0a3069; }
+.hl-str { color: #015b2f; }
+.hl-cmt { color: #6a737d; font-style: italic; }
+```
+
+---
+
+#### API Summary
+
+- `@Composable fun EditorWithOverlay(code: String, setCode: (String) -> Unit, tabSize: Int = 4, onKeyDown: ((SyntheticKeyboardEvent) -> Unit)? = null)`
+  - Pure editor, no actions. Wire your own buttons and shortcuts.
+  - Self-contained styling, adjustable with your own CSS if desired.
+
+- `fun ensureBootstrapCodeBlocks(html: String): String`
+  - Adds `class="code"` to `<pre>` tags if not present.
+
+- `fun highlightLyngHtml(html: String): String`
+  - Highlights Lyng `<code class="language-lyng">...</code>` blocks inside the provided HTML.
+
+- `fun htmlEscape(s: String): String`
+  - Escapes special HTML characters.
+
+- `object net.sergeych.site.SiteHighlight`
+  - `fun renderHtml(text: String): String` — renders highlighted spans with `hl-*` classes; kept for compatibility with existing site code/tests.
+
+---
+
+#### Notes
+
+- The editor does not ship default color styles for `hl-*` classes. Provide your own CSS to match your theme.
+- If you want a minimal look without Bootstrap, the editor still works out of the box due to inline styles.

lyngweb/build.gradle.kts

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+/*
+ * Copyright 2025 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+/*
+ * JS library module providing Lyng web UI components and HTML highlighter
+ */
+
+plugins {
+    alias(libs.plugins.kotlinMultiplatform)
+    id("org.jetbrains.kotlin.plugin.compose") version "2.2.21"
+    id("org.jetbrains.compose") version "1.9.3"
+}
+
+kotlin {
+    js(IR) {
+        browser {
+            commonWebpackConfig {
+                cssSupport { enabled.set(true) }
+            }
+        }
+        binaries.library()
+    }
+
+    sourceSets {
+        val jsMain by getting {
+            dependencies {
+                implementation("org.jetbrains.compose.runtime:runtime:1.9.3")
+                implementation("org.jetbrains.compose.html:html-core:1.9.3")
+                implementation(libs.kotlinx.coroutines.core)
+                implementation(project(":lynglib"))
+            }
+        }
+        val jsTest by getting {
+            dependencies { implementation(libs.kotlin.test) }
+        }
+    }
+}

lyngweb/src/jsMain/kotlin/net/sergeych/lyngweb/Editor.kt

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+/*
+ * Copyright 2025 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package net.sergeych.lyngweb
+
+import androidx.compose.runtime.*
+import kotlinx.browser.window
+import net.sergeych.site.SiteHighlight
+import org.jetbrains.compose.web.attributes.placeholder
+import org.jetbrains.compose.web.dom.Div
+import org.jetbrains.compose.web.events.SyntheticKeyboardEvent
+import org.w3c.dom.HTMLElement
+import org.w3c.dom.HTMLTextAreaElement
+
+/**
+ * A lightweight, dependency-free code editor for Compose HTML that renders syntax highlight
+ * in an overlay while keeping the native textarea for input and caret/selection.
+ *
+ * Features:
+ * - Pure editor: no built-in buttons or actions; wire shortcuts via [onKeyDown].
+ * - Tab insertion and smart newline indentation.
+ * - Keeps overlay scroll, paddings, and line-height in sync with the textarea for glyph alignment.
+ * - No external CSS dependency: all essential styles are injected inline.
+ *
+ * Parameters:
+ * - [code]: current text value.
+ * - [setCode]: callback to update text.
+ * - [tabSize]: number of spaces to insert on Tab and used for visual tab width.
+ * - [onKeyDown]: optional raw keydown hook to handle shortcuts like Ctrl/Cmd+Enter.
+ */
+@Composable
+fun EditorWithOverlay(
+    code: String,
+    setCode: (String) -> Unit,
+    tabSize: Int = 4,
+    onKeyDown: ((SyntheticKeyboardEvent) -> Unit)? = null,
+) {
+    var overlayEl by remember { mutableStateOf<HTMLElement?>(null) }
+    var taEl by remember { mutableStateOf<HTMLTextAreaElement?>(null) }
+    var lastGoodHtml by remember { mutableStateOf<String?>(null) }
+    var lastGoodText by remember { mutableStateOf<String?>(null) }
+    var pendingSelStart by remember { mutableStateOf<Int?>(null) }
+    var pendingSelEnd by remember { mutableStateOf<Int?>(null) }
+    var pendingScrollTop by remember { mutableStateOf<Double?>(null) }
+    var pendingScrollLeft by remember { mutableStateOf<Double?>(null) }
+
+    // Update overlay HTML whenever code changes
+    LaunchedEffect(code) {
+        fun htmlEscapeLocal(s: String): String = buildString(s.length) {
+            for (ch in s) when (ch) {
+                '<' -> append("&lt;")
+                '>' -> append("&gt;")
+                '&' -> append("&amp;")
+                '"' -> append("&quot;")
+                '\'' -> append("&#39;")
+                else -> append(ch)
+            }
+        }
+
+        fun trimHtmlToTextPrefix(html: String, prefixChars: Int): String {
+            if (prefixChars <= 0) return ""
+            var i = 0
+            var textCount = 0
+            val n = html.length
+            val out = StringBuilder(prefixChars + 64)
+            val stack = mutableListOf<String>()
+            while (i < n && textCount < prefixChars) {
+                val ch = html[i]
+                if (ch == '<') {
+                    val close = html.indexOf('>', i)
+                    if (close == -1) break
+                    val tag = html.substring(i, close + 1)
+                    out.append(tag)
+                    val tagLower = tag.lowercase()
+                    if (tagLower.startsWith("<span")) {
+                        stack.add("</span>")
+                    } else if (tagLower.startsWith("</span")) {
+                        if (stack.isNotEmpty()) stack.removeAt(stack.lastIndex)
+                    }
+                    i = close + 1
+                } else if (ch == '&') {
+                    val semi = html.indexOf(';', i + 1).let { if (it == -1) n - 1 else it }
+                    val entity = html.substring(i, semi + 1)
+                    out.append(entity)
+                    textCount += 1
+                    i = semi + 1
+                } else {
+                    out.append(ch)
+                    textCount += 1
+                    i += 1
+                }
+            }
+            for (j in stack.size - 1 downTo 0) out.append(stack[j])
+            return out.toString()
+        }
+
+        fun appendSentinel(html: String): String =
+            html + "<span data-sentinel=\"1\">&#8203;</span>"
+
+        try {
+            val html = SiteHighlight.renderHtml(code)
+            overlayEl?.innerHTML = appendSentinel(html)
+            lastGoodHtml = html
+            lastGoodText = code
+        } catch (_: Throwable) {
+            val prevHtml = lastGoodHtml
+            val prevText = lastGoodText
+            if (prevHtml != null && prevText != null) {
+                val max = minOf(prevText.length, code.length)
+                var k = 0
+                while (k < max && prevText[k] == code[k]) k++
+                val prefixLen = k
+                val trimmed = trimHtmlToTextPrefix(prevHtml, prefixLen)
+                val tail = code.substring(prefixLen)
+                val combined = trimmed + htmlEscapeLocal(tail)
+                overlayEl?.innerHTML = appendSentinel(combined)
+            } else {
+                overlayEl?.innerHTML = appendSentinel(htmlEscapeLocal(code))
+            }
+        }
+
+        val st = pendingScrollTop ?: (taEl?.scrollTop ?: 0.0)
+        val sl = pendingScrollLeft ?: (taEl?.scrollLeft ?: 0.0)
+        overlayEl?.scrollTop = st
+        overlayEl?.scrollLeft = sl
+        pendingScrollTop = null
+        pendingScrollLeft = null
+    }
+
+    fun setSelection(start: Int, end: Int = start) {
+        (taEl ?: return).apply {
+            selectionStart = start
+            selectionEnd = end
+            focus()
+        }
+    }
+
+    Div({
+        // avoid external CSS dependency: ensure base positioning inline
+        classes("position-relative")
+        attr("style", "position:relative;")
+    }) {
+        // Overlay: highlighted code
+        org.jetbrains.compose.web.dom.Div({
+            // Do not depend on any external class name like "editor-overlay"
+            // Provide fully inline styling; classes left empty to avoid external deps
+            attr(
+                "style",
+                buildString {
+                    append("position:absolute; left:0; top:0; right:0; bottom:0;")
+                    append("overflow:auto; box-sizing:border-box; white-space:pre-wrap; word-break:break-word; tab-size:")
+                    append(tabSize)
+                    append("; margin:0; pointer-events:none; font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, \"Liberation Mono\", \"Courier New\", monospace;")
+                }
+            )
+            ref { it ->
+                overlayEl = it
+                onDispose { if (overlayEl === it) overlayEl = null }
+            }
+        }) {}
+
+        // Textarea: user input with transparent text
+        org.jetbrains.compose.web.dom.TextArea(value = code, attrs = {
+            ref { ta ->
+                taEl = ta
+                onDispose { if (taEl === ta) taEl = null }
+            }
+            // Avoid relying on external classes; still allow host app to override via CSS
+            // Make typed text transparent (overlay renders the colored text), but keep caret visible
+            attr(
+                "style",
+                buildString {
+                    append("width:100%; min-height:220px; background:transparent; position:relative; z-index:1; tab-size:")
+                    append(tabSize)
+                    append("; color:transparent; -webkit-text-fill-color:transparent; ")
+                    // Make caret visible even though text color is transparent
+                    append("caret-color: var(--bs-body-color, #212529);")
+                    // Basic input look without relying on external CSS
+                    append(" border: 1px solid var(--bs-border-color, #ced4da); border-radius: .375rem;")
+                    append(" padding: .5rem .75rem; box-sizing: border-box;")
+                    // Remove UA focus outline that may appear as a red border in some themes
+                    append(" outline: none; box-shadow: none;")
+                    // Typography and rendering
+                    append(" font-variant-ligatures: none; font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, \"Liberation Mono\", \"Courier New\", monospace;")
+                }
+            )
+            // Disable browser corrections for a code editor
+            attr("spellcheck", "false")
+            attr("autocorrect", "off")
+            attr("autocapitalize", "off")
+            attr("autocomplete", "off")
+            placeholder("Enter Lyng code here…")
+
+            onInput { ev ->
+                val v = (ev.target as HTMLTextAreaElement).value
+                setCode(v)
+            }
+
+            onKeyDown { ev ->
+                // bubble to caller first so they may intercept shortcuts
+                onKeyDown?.invoke(ev)
+                val ta = taEl ?: return@onKeyDown
+                val key = ev.key
+                if (key == "Tab") {
+                    ev.preventDefault()
+                    val start = ta.selectionStart ?: 0
+                    val end = ta.selectionEnd ?: start
+                    val current = ta.value
+                    val before = current.substring(0, start)
+                    val after = current.substring(end)
+                    val spaces = " ".repeat(tabSize)
+                    val updated = before + spaces + after
+                    pendingSelStart = start + spaces.length
+                    pendingSelEnd = pendingSelStart
+                    setCode(updated)
+                } else if (key == "Enter") {
+                    // Smart indent: copy leading spaces from current line
+                    val start = ta.selectionStart ?: 0
+                    val cur = ta.value
+                    val lineStart = run {
+                        var i = start - 1
+                        while (i >= 0 && cur[i] != '\n') i--
+                        i + 1
+                    }
+                    var indent = 0
+                    while (lineStart + indent < cur.length && cur[lineStart + indent] == ' ') indent++
+                    val before = cur.substring(0, start)
+                    val after = cur.substring(start)
+                    val insertion = "\n" + " ".repeat(indent)
+                    pendingSelStart = start + insertion.length
+                    pendingSelEnd = pendingSelStart
+                    setCode(before + insertion + after)
+                    ev.preventDefault()
+                }
+            }
+
+            onScroll { ev ->
+                val src = ev.target as? HTMLTextAreaElement ?: return@onScroll
+                overlayEl?.scrollTop = src.scrollTop
+                overlayEl?.scrollLeft = src.scrollLeft
+            }
+        })
+
+        // No built-in action buttons: EditorWithOverlay is a pure editor now
+    }
+
+    // Ensure overlay typography and paddings mirror the textarea so characters line up 1:1
+    LaunchedEffect(taEl, overlayEl) {
+        try {
+            val ta = taEl ?: return@LaunchedEffect
+            val ov = overlayEl ?: return@LaunchedEffect
+            val cs = window.getComputedStyle(ta)
+
+            // Best-effort concrete line-height
+            val lineHeight = cs.lineHeight.takeIf { it.endsWith("px") } ?: cs.fontSize
+
+            val style = buildString {
+                append("position:absolute; inset:0; overflow:auto; pointer-events:none; box-sizing:border-box;")
+                append(" white-space:pre-wrap; word-break:break-word; tab-size:")
+                append(tabSize)
+                append(";")
+                append("font-family:").append(cs.fontFamily).append(';')
+                append("font-size:").append(cs.fontSize).append(';')
+                if (!lineHeight.isNullOrBlank()) append("line-height:").append(lineHeight).append(';')
+                append("letter-spacing:").append(cs.letterSpacing).append(';')
+                // keep visual rendering close to textarea
+                append("font-variant-ligatures:none; -webkit-font-smoothing:antialiased; text-rendering:optimizeSpeed;")
+                // mirror paddings
+                append("padding-top:").append(cs.paddingTop).append(';')
+                append("padding-right:").append(cs.paddingRight).append(';')
+                append("padding-bottom:").append(cs.paddingBottom).append(';')
+                append("padding-left:").append(cs.paddingLeft).append(';')
+                // base color in case we render plain text fallback
+                append("color: var(--bs-body-color);")
+            }
+            ov.setAttribute("style", style)
+            // also enforce concrete line-height on textarea to stabilize caret metrics
+            val existing = ta.getAttribute("style") ?: ""
+            if (!existing.contains("line-height") && !lineHeight.isNullOrBlank()) {
+                ta.setAttribute("style", existing + " line-height: " + lineHeight + ";")
+            }
+        } catch (_: Throwable) {
+        }
+    }
+
+    // Apply pending selection when value updates
+    LaunchedEffect(code, pendingSelStart, pendingSelEnd) {
+        val s = pendingSelStart
+        val e = pendingSelEnd
+        if (s != null && e != null) {
+            pendingSelStart = null
+            pendingSelEnd = null
+            window.setTimeout({ setSelection(s, e) }, 0)
+        }
+    }
+}

lyngweb/src/jsMain/kotlin/net/sergeych/lyngweb/Highlight.kt

@@ -0,0 +1,265 @@
+/*
+ * Copyright 2025 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+/*
+ * Shared Lyng HTML highlighting utilities for Compose HTML apps
+ */
+package net.sergeych.lyngweb
+
+import net.sergeych.lyng.highlight.HighlightKind
+import net.sergeych.lyng.highlight.SimpleLyngHighlighter
+
+/**
+ * Adds a Bootstrap-friendly `code` class to every opening `<pre>` tag in the provided HTML.
+ *
+ * This is a lightweight post-processing step for Markdown-rendered HTML to ensure that
+ * code blocks (wrapped in `<pre>...</pre>`) receive consistent styling in Bootstrap-based
+ * sites without requiring changes in the Markdown renderer.
+ *
+ * Behavior:
+ * - If a `<pre>` has no `class` attribute, a `class="code"` attribute is added.
+ * - If a `<pre>` already has a `class` attribute but not `code`, the word `code` is appended.
+ * - Other attributes and their order are preserved.
+ *
+ * Example:
+ * ```kotlin
+ * val withClasses = ensureBootstrapCodeBlocks("<pre><code>println(1)</code></pre>")
+ * // => "<pre class=\"code\"><code>println(1)</code></pre>"
+ * ```
+ *
+ * @param html HTML text to transform.
+ * @return HTML with `<pre>` tags normalized to include the `code` class.
+ */
+fun ensureBootstrapCodeBlocks(html: String): String {
+    val preTagRegex = Regex("""<pre(\s+[^>]*)?>""", RegexOption.IGNORE_CASE)
+    val classAttrRegex = Regex("""\bclass\s*=\s*(["'])(.*?)\1""", RegexOption.IGNORE_CASE)
+
+    return preTagRegex.replace(html) { match ->
+        val attrs = match.groups[1]?.value ?: ""
+        if (attrs.isBlank()) return@replace "<pre class=\"code\">"
+
+        var newAttrs = attrs
+        val m = classAttrRegex.find(attrs)
+        if (m != null) {
+            val quote = m.groupValues[1]
+            val classes = m.groupValues[2]
+            val hasCode = classes.split("\\s+".toRegex()).any { it == "code" }
+            if (!hasCode) {
+                val updated = "class=" + quote + (classes.trim().let { if (it.isEmpty()) "code" else "$it code" }) + quote
+                newAttrs = attrs.replaceRange(m.range, updated)
+            }
+        } else {
+            newAttrs = " class=\"code\"" + attrs
+        }
+        "<pre$newAttrs>"
+    }
+}
+
+/**
+ * Highlights Lyng code blocks inside Markdown-produced HTML.
+ *
+ * Searches for sequences of `<pre><code ...>...</code></pre>` and, if the `<code>` element
+ * carries class `language-lyng` (or if it has no `language-*` class at all), applies Lyng
+ * syntax highlighting, replacing the inner HTML with spans that use `hl-*` CSS classes
+ * (e.g. `hl-kw`, `hl-id`, `hl-num`, `hl-cmt`).
+ *
+ * Special handling:
+ * - If a block has no explicit language class, doctest-style result lines starting with
+ *   `>>>` at the end of the block are rendered as comments (`hl-cmt`).
+ * - If the block specifies another language (e.g. `language-kotlin`), the block is left
+ *   unchanged.
+ *
+ * Example:
+ * ```kotlin
+ * val mdHtml = """
+ *   <pre><code class=\"language-lyng\">and or not\n</code></pre>
+ * """.trimIndent()
+ * val highlighted = highlightLyngHtml(mdHtml)
+ * ```
+ *
+ * @param html HTML produced by a Markdown renderer.
+ * @return HTML with Lyng code blocks highlighted using `hl-*` classes.
+ */
+fun highlightLyngHtml(html: String): String {
+    // Regex to find <pre> ... <code class="language-lyng ...">(content)</code> ... </pre>
+    val preCodeRegex = Regex(
+        pattern = """<pre(\s+[^>]*)?>\s*<code([^>]*)>([\s\S]*?)</code>\s*</pre>""",
+        options = setOf(RegexOption.IGNORE_CASE)
+    )
+    val classAttrRegex = Regex("""\bclass\s*=\s*(["'])(.*?)\1""", RegexOption.IGNORE_CASE)
+
+    return preCodeRegex.replace(html) { m ->
+        val preAttrs = m.groups[1]?.value ?: ""
+        val codeAttrs = m.groups[2]?.value ?: ""
+        val codeHtml = m.groups[3]?.value ?: ""
+
+        val codeHasLyng = run {
+            val cls = classAttrRegex.find(codeAttrs)?.groupValues?.getOrNull(2) ?: ""
+            cls.split("\\s+".toRegex()).any { it.equals("language-lyng", ignoreCase = true) }
+        }
+        val hasAnyLanguage = run {
+            val cls = classAttrRegex.find(codeAttrs)?.groupValues?.getOrNull(2) ?: ""
+            cls.split("\\s+".toRegex()).any { it.startsWith("language-", ignoreCase = true) }
+        }
+
+        val treatAsLyng = codeHasLyng || !hasAnyLanguage
+        if (!treatAsLyng) return@replace m.value
+
+        val text = htmlUnescape(codeHtml)
+
+        val (headText, tailTextOrNull) = if (!codeHasLyng && !hasAnyLanguage) splitDoctestTail(text) else text to null
+
+        val headHighlighted = try {
+            applyLyngHighlightToText(headText)
+        } catch (_: Throwable) {
+            return@replace m.value
+        }
+        val tailHighlighted = tailTextOrNull?.let { renderDoctestTailAsComments(it) } ?: ""
+
+        val highlighted = headHighlighted + tailHighlighted
+        "<pre$preAttrs><code$codeAttrs>$highlighted</code></pre>"
+    }
+}
+
+private fun splitDoctestTail(text: String): Pair<String, String?> {
+    if (text.isEmpty()) return "" to null
+    val hasTrailingNewline = text.endsWith("\n")
+    val lines = text.split("\n")
+    var i = lines.size - 1
+    while (i >= 0 && lines[i].isEmpty()) i--
+    var count = 0
+    while (i >= 0) {
+        val line = lines[i]
+        val trimmed = line.trimStart()
+        if (trimmed.isNotEmpty() && !trimmed.startsWith(">>>")) break
+        if (trimmed.isEmpty()) {
+            if (count == 0) break else { count++; i--; continue }
+        }
+        count++
+        i--
+    }
+    if (count == 0) return text to null
+    val splitIndex = lines.size - count
+    val head = buildString {
+        for (idx in 0 until splitIndex) {
+            append(lines[idx])
+            if (idx < lines.size - 1 || hasTrailingNewline) append('\n')
+        }
+    }
+    val tail = buildString {
+        for (idx in splitIndex until lines.size) {
+            append(lines[idx])
+            if (idx < lines.size - 1 || hasTrailingNewline) append('\n')
+        }
+    }
+    return head to tail
+}
+
+private fun renderDoctestTailAsComments(tail: String): String {
+    if (tail.isEmpty()) return ""
+    val sb = StringBuilder(tail.length + 32)
+    var start = 0
+    while (start <= tail.lastIndex) {
+        val nl = tail.indexOf('\n', start)
+        val line = if (nl >= 0) tail.substring(start, nl) else tail.substring(start)
+        sb.append("<span class=\"hl-cmt\">")
+        sb.append(htmlEscape(line))
+        sb.append("</span>")
+        if (nl >= 0) sb.append('\n')
+        if (nl < 0) break else start = nl + 1
+    }
+    return sb.toString()
+}
+
+/**
+ * Converts plain Lyng source text into HTML with syntax-highlight spans.
+ *
+ * Tokens are wrapped in `<span>` elements with `hl-*` classes (e.g., `hl-kw`, `hl-id`).
+ * Text between tokens is HTML-escaped and preserved. If no tokens are detected,
+ * the whole text is returned HTML-escaped.
+ *
+ * This is a low-level utility used by [highlightLyngHtml]. If you already have
+ * Markdown-produced HTML with `<pre><code>` blocks, prefer calling [highlightLyngHtml].
+ *
+ * @param text Lyng source code (plain text, not HTML-escaped).
+ * @return HTML string with `hl-*` spans.
+ */
+fun applyLyngHighlightToText(text: String): String {
+    val spans = SimpleLyngHighlighter().highlight(text)
+    if (spans.isEmpty()) return htmlEscape(text)
+    val sb = StringBuilder(text.length + spans.size * 16)
+    var pos = 0
+    for (s in spans) {
+        if (s.range.start > pos) sb.append(htmlEscape(text.substring(pos, s.range.start)))
+        val cls = cssClassForKind(s.kind)
+        sb.append('<').append("span class=\"").append(cls).append('\"').append('>')
+        sb.append(htmlEscape(text.substring(s.range.start, s.range.endExclusive)))
+        sb.append("</span>")
+        pos = s.range.endExclusive
+    }
+    if (pos < text.length) sb.append(htmlEscape(text.substring(pos)))
+    return sb.toString()
+}
+
+private fun cssClassForKind(kind: HighlightKind): String = when (kind) {
+    HighlightKind.Keyword -> "hl-kw"
+    HighlightKind.TypeName -> "hl-ty"
+    HighlightKind.Identifier -> "hl-id"
+    HighlightKind.Number -> "hl-num"
+    HighlightKind.String -> "hl-str"
+    HighlightKind.Char -> "hl-ch"
+    HighlightKind.Regex -> "hl-rx"
+    HighlightKind.Comment -> "hl-cmt"
+    HighlightKind.Operator -> "hl-op"
+    HighlightKind.Punctuation -> "hl-punc"
+    HighlightKind.Label -> "hl-lbl"
+    HighlightKind.Directive -> "hl-dir"
+    HighlightKind.Error -> "hl-err"
+}
+
+/**
+ * Escapes special HTML characters in a plain text string.
+ *
+ * Replacements:
+ * - `&` → `&amp;`
+ * - `<` → `&lt;`
+ * - `>` → `&gt;`
+ * - `"` → `&quot;`
+ * - `'` → `&#39;`
+ *
+ * @param s Text to escape.
+ * @return HTML-escaped text safe to insert into an HTML context.
+ */
+fun htmlEscape(s: String): String = buildString(s.length) {
+    for (ch in s) when (ch) {
+        '<' -> append("&lt;")
+        '>' -> append("&gt;")
+        '&' -> append("&amp;")
+        '"' -> append("&quot;")
+        '\'' -> append("&#39;")
+        else -> append(ch)
+    }
+}
+
+private fun htmlUnescape(s: String): String {
+    return s
+        .replace("&lt;", "<")
+        .replace("&gt;", ">")
+        .replace("&amp;", "&")
+        .replace("&quot;", "\"")
+        .replace("&#39;", "'")
+}

lyngweb/src/jsMain/kotlin/net/sergeych/site/SiteHighlight.kt

@@ -0,0 +1,87 @@
+/*
+ * Copyright 2025 Sergey S. Chernov real.sergeych@gmail.com
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+/*
+ * Site-like wrapper for Lyng highlighter that renders HTML spans with CSS classes
+ * compatible with the site styles. Kept in package net.sergeych.site for backwards
+ * compatibility with existing code and tests.
+ */
+package net.sergeych.site
+
+import net.sergeych.lyng.highlight.HighlightKind
+import net.sergeych.lyng.highlight.SimpleLyngHighlighter
+import net.sergeych.lyngweb.htmlEscape
+
+/**
+ * Minimal HTML renderer for Lyng syntax highlighting, compatible with the site CSS.
+ *
+ * This object is kept in the legacy package `net.sergeych.site` to preserve
+ * backward compatibility with existing imports and tests in dependent modules.
+ * It renders spans with the `hl-*` classes used by the site (e.g., `hl-kw`,
+ * `hl-id`, `hl-num`).
+ */
+object SiteHighlight {
+    private fun cssClassForKind(kind: HighlightKind): String = when (kind) {
+        HighlightKind.Keyword -> "hl-kw"
+        HighlightKind.TypeName -> "hl-ty"
+        HighlightKind.Identifier -> "hl-id"
+        HighlightKind.Number -> "hl-num"
+        HighlightKind.String -> "hl-str"
+        HighlightKind.Char -> "hl-ch"
+        HighlightKind.Regex -> "hl-rx"
+        HighlightKind.Comment -> "hl-cmt"
+        HighlightKind.Operator -> "hl-op"
+        HighlightKind.Punctuation -> "hl-punc"
+        HighlightKind.Label -> "hl-lbl"
+        HighlightKind.Directive -> "hl-dir"
+        HighlightKind.Error -> "hl-err"
+    }
+
+    /**
+     * Converts plain Lyng source [text] into HTML with `<span>` wrappers using
+     * site-compatible `hl-*` classes.
+     *
+     * Non-highlighted parts are HTML-escaped. If the highlighter returns no
+     * tokens, the entire string is returned as an escaped plain text.
+     *
+     * Example:
+     * ```kotlin
+     * val html = SiteHighlight.renderHtml("assertEquals(1, 1)")
+     * // => "<span class=\"hl-id\">assertEquals</span><span class=\"hl-punc\">(</span>..."
+     * ```
+     *
+     * @param text Lyng code to render (plain text).
+     * @return HTML string with `hl-*` styled tokens.
+     */
+    fun renderHtml(text: String): String {
+        val highlighter = SimpleLyngHighlighter()
+        val spans = highlighter.highlight(text)
+        if (spans.isEmpty()) return htmlEscape(text)
+        val sb = StringBuilder(text.length + spans.size * 16)
+        var pos = 0
+        for (s in spans) {
+            if (s.range.start > pos) sb.append(htmlEscape(text.substring(pos, s.range.start)))
+            val cls = cssClassForKind(s.kind)
+            sb.append('<').append("span class=\"").append(cls).append('\"').append('>')
+            sb.append(htmlEscape(text.substring(s.range.start, s.range.endExclusive)))
+            sb.append("</span>")
+            pos = s.range.endExclusive
+        }
+        if (pos < text.length) sb.append(htmlEscape(text.substring(pos)))
+        return sb.toString()
+    }
+}

settings.gradle.kts

@@ -37,3 +37,4 @@ rootProject.name = "lyng"
 include(":lynglib")
 include(":lyng")
 include(":site")
+include(":lyngweb")

site/build.gradle.kts

@@ -51,6 +51,8 @@ kotlin {
                 implementation(libs.kotlinx.coroutines.core)
                 // Lyng highlighter (common, used from JS)
                 implementation(project(":lynglib"))
+                // Shared web editor and highlighting utilities
+                implementation(project(":lyngweb"))
                 // Markdown parser (NPM)
                 implementation(npm("marked", "12.0.2"))
                 // Self-host MathJax via npm and bundle it with webpack

site/src/jsMain/kotlin/HighlightSupport.kt

@@ -24,7 +24,10 @@ package net.sergeych.site
 import net.sergeych.lyng.highlight.HighlightKind
 import net.sergeych.lyng.highlight.SimpleLyngHighlighter
 
-object SiteHighlight {
+// Kept only to avoid breaking imports if any remain; actual implementation moved to :lyngweb
+// Use net.sergeych.site.SiteHighlight from :lyngweb instead. This local copy is renamed and unused.
+@Deprecated("Use lyngweb: net.sergeych.site.SiteHighlight")
+object SiteHighlightLocal {
     private fun cssClassForKind(kind: HighlightKind): String = when (kind) {
         HighlightKind.Keyword -> "hl-kw"
         HighlightKind.TypeName -> "hl-ty"

site/src/jsMain/kotlin/HomePage.kt

@@ -16,6 +16,9 @@
  */
 
 import androidx.compose.runtime.Composable
+import net.sergeych.lyngweb.ensureBootstrapCodeBlocks
+import net.sergeych.lyngweb.highlightLyngHtml
+import net.sergeych.lyngweb.htmlEscape
 import org.jetbrains.compose.web.dom.*
 
 @Composable

site/src/jsMain/kotlin/Main.kt

@@ -304,8 +304,8 @@ fun highlightSearchHits(root: HTMLElement, terms: List<String>): Int {
 }
 
 fun renderMarkdown(src: String): String =
-    highlightLyngHtml(
+    net.sergeych.lyngweb.highlightLyngHtml(
-        ensureBootstrapCodeBlocks(
+        net.sergeych.lyngweb.ensureBootstrapCodeBlocks(
             ensureBootstrapTables(
                 ensureDefinitionLists(
                     marked.parse(src)
@@ -929,177 +929,7 @@ fun ensureBootstrapCodeBlocks(html: String): String {
     }
 }
 
-// ---- Lyng syntax highlighting over rendered HTML ----
+// moved highlighting utilities to :lyngweb
-// This post-processor finds <pre><code class="language-lyng">…</code></pre> blocks and replaces the
-// inner code HTML with token-wrapped spans using the common Lyng highlighter.
-// It performs a minimal HTML entity decode on the code content to obtain the original text,
-// runs the highlighter, then escapes segments back and wraps with <span class="hl-…">.
-internal fun highlightLyngHtml(html: String): String {
-    // Regex to find <pre> ... <code class="language-lyng ...">(content)</code> ... </pre>
-    val preCodeRegex = Regex(
-        pattern = """<pre(\s+[^>]*)?>\s*<code([^>]*)>([\s\S]*?)</code>\s*</pre>""",
-        options = setOf(RegexOption.IGNORE_CASE)
-    )
-    val classAttrRegex = Regex("""\bclass\s*=\s*(["'])(.*?)\1""", RegexOption.IGNORE_CASE)
-
-    return preCodeRegex.replace(html) { m ->
-        val preAttrs = m.groups[1]?.value ?: ""
-        val codeAttrs = m.groups[2]?.value ?: ""
-        val codeHtml = m.groups[3]?.value ?: ""
-
-        val codeHasLyng = run {
-            val cls = classAttrRegex.find(codeAttrs)?.groupValues?.getOrNull(2) ?: ""
-            cls.split("\\s+".toRegex()).any { it.equals("language-lyng", ignoreCase = true) }
-        }
-        // If not explicitly Lyng, check if the <code> has any language class; if none, treat as Lyng by default
-        val hasAnyLanguage = run {
-            val cls = classAttrRegex.find(codeAttrs)?.groupValues?.getOrNull(2) ?: ""
-            cls.split("\\s+".toRegex()).any { it.startsWith("language-", ignoreCase = true) }
-        }
-
-        val treatAsLyng = codeHasLyng || !hasAnyLanguage
-        if (!treatAsLyng) return@replace m.value // leave untouched for non-Lyng languages
-
-        val text = htmlUnescape(codeHtml)
-
-        // If block has no explicit language (unfenced/indented), support doctest tail (trailing lines starting with ">>>")
-        val (headText, tailTextOrNull) = if (!codeHasLyng && !hasAnyLanguage) splitDoctestTail(text) else text to null
-
-        val headHighlighted = try {
-            applyLyngHighlightToText(headText)
-        } catch (_: Throwable) {
-            return@replace m.value
-        }
-        val tailHighlighted = tailTextOrNull?.let { renderDoctestTailAsComments(it) } ?: ""
-
-        val highlighted = headHighlighted + tailHighlighted
-
-        // Preserve original attrs; ensure <pre> has existing attrs (Bootstrap '.code' was handled earlier)
-        "<pre$preAttrs><code$codeAttrs>$highlighted</code></pre>"
-    }
-}
-
-// Split trailing doctest tail: consecutive lines at the end whose trimmedStart starts with ">>>".
-// Returns Pair(head, tail) where tail is null if no doctest lines found.
-private fun splitDoctestTail(text: String): Pair<String, String?> {
-    if (text.isEmpty()) return "" to null
-    // Normalize to \n for splitting; remember if original ended with newline
-    val hasTrailingNewline = text.endsWith("\n")
-    val lines = text.split("\n")
-    var i = lines.size - 1
-    // Skip trailing completely empty lines before looking for doctest markers
-    while (i >= 0 && lines[i].isEmpty()) i--
-    var count = 0
-    while (i >= 0) {
-        val line = lines[i]
-        // If last line is empty due to trailing newline, include it into tail only if there are already doctest lines
-        val trimmed = line.trimStart()
-        if (trimmed.isNotEmpty() && !trimmed.startsWith(">>>")) break
-        // Accept empty line only if it follows some doctest lines (keeps spacing), else stop
-        if (trimmed.isEmpty()) {
-            if (count == 0) break else { count++; i--; continue }
-        }
-        // doctest line
-        count++
-        i--
-    }
-    if (count == 0) return text to null
-    val splitIndex = lines.size - count
-    val head = buildString {
-        for (idx in 0 until splitIndex) {
-            append(lines[idx])
-            if (idx < lines.size - 1 || hasTrailingNewline) append('\n')
-        }
-    }
-    val tail = buildString {
-        for (idx in splitIndex until lines.size) {
-            append(lines[idx])
-            if (idx < lines.size - 1 || hasTrailingNewline) append('\n')
-        }
-    }
-    return head to tail
-}
-
-// Render the doctest tail as comment-highlighted lines. Expects the original textual tail including newlines.
-private fun renderDoctestTailAsComments(tail: String): String {
-    if (tail.isEmpty()) return ""
-    val sb = StringBuilder(tail.length + 32)
-    var start = 0
-    while (start <= tail.lastIndex) {
-        val nl = tail.indexOf('\n', start)
-        val line = if (nl >= 0) tail.substring(start, nl) else tail.substring(start)
-        // Wrap the whole line in comment styling
-        sb.append("<span class=\"hl-cmt\">")
-        sb.append(htmlEscape(line))
-        sb.append("</span>")
-        if (nl >= 0) sb.append('\n')
-        if (nl < 0) break else start = nl + 1
-    }
-    return sb.toString()
-}
-
-// Apply Lyng highlighter to raw code text, producing HTML with span classes.
-internal fun applyLyngHighlightToText(text: String): String {
-    val highlighter = net.sergeych.lyng.highlight.SimpleLyngHighlighter()
-    // Use spans as produced by the fixed lynglib highlighter (comments already extend to EOL there)
-    val spans = highlighter.highlight(text)
-    if (spans.isEmpty()) return htmlEscape(text)
-    val sb = StringBuilder(text.length + spans.size * 16)
-    var pos = 0
-    for (s in spans) {
-        if (s.range.start > pos) {
-            sb.append(htmlEscape(text.substring(pos, s.range.start)))
-        }
-        val cls = cssClassForKind(s.kind)
-        sb.append('<').append("span class=\"").append(cls).append('\"').append('>')
-        sb.append(htmlEscape(text.substring(s.range.start, s.range.endExclusive)))
-        sb.append("</span>")
-        pos = s.range.endExclusive
-    }
-    if (pos < text.length) sb.append(htmlEscape(text.substring(pos)))
-    return sb.toString()
-}
-
-// Note: No site-side span post-processing — we rely on lynglib's SimpleLyngHighlighter for correctness.
-
-private fun cssClassForKind(kind: net.sergeych.lyng.highlight.HighlightKind): String = when (kind) {
-    net.sergeych.lyng.highlight.HighlightKind.Keyword -> "hl-kw"
-    net.sergeych.lyng.highlight.HighlightKind.TypeName -> "hl-ty"
-    net.sergeych.lyng.highlight.HighlightKind.Identifier -> "hl-id"
-    net.sergeych.lyng.highlight.HighlightKind.Number -> "hl-num"
-    net.sergeych.lyng.highlight.HighlightKind.String -> "hl-str"
-    net.sergeych.lyng.highlight.HighlightKind.Char -> "hl-ch"
-    net.sergeych.lyng.highlight.HighlightKind.Regex -> "hl-rx"
-    net.sergeych.lyng.highlight.HighlightKind.Comment -> "hl-cmt"
-    net.sergeych.lyng.highlight.HighlightKind.Operator -> "hl-op"
-    net.sergeych.lyng.highlight.HighlightKind.Punctuation -> "hl-punc"
-    net.sergeych.lyng.highlight.HighlightKind.Label -> "hl-lbl"
-    net.sergeych.lyng.highlight.HighlightKind.Directive -> "hl-dir"
-    net.sergeych.lyng.highlight.HighlightKind.Error -> "hl-err"
-}
-
-// Minimal HTML escaping for text nodes
-fun htmlEscape(s: String): String = buildString(s.length) {
-    for (ch in s) when (ch) {
-        '<' -> append("&lt;")
-        '>' -> append("&gt;")
-        '&' -> append("&amp;")
-        '"' -> append("&quot;")
-        '\'' -> append("&#39;")
-        else -> append(ch)
-    }
-}
-
-// Minimal unescape for code inner HTML produced by marked
-private fun htmlUnescape(s: String): String {
-    // handle common entities only
-    return s
-        .replace("&lt;", "<")
-        .replace("&gt;", ">")
-        .replace("&amp;", "&")
-        .replace("&quot;", "\"")
-        .replace("&#39;", "'")
-}
 
 fun rewriteImages(root: HTMLElement, basePath: String) {
     val imgs = root.querySelectorAll("img")

site/src/jsMain/kotlin/TryLyngPage.kt

@@ -16,15 +16,11 @@
  */
 
 import androidx.compose.runtime.*
-import kotlinx.browser.window
 import kotlinx.coroutines.launch
 import net.sergeych.lyng.Scope
 import net.sergeych.lyng.ScriptError
-import net.sergeych.site.SiteHighlight
+import net.sergeych.lyngweb.EditorWithOverlay
-import org.jetbrains.compose.web.attributes.placeholder
 import org.jetbrains.compose.web.dom.*
-import org.w3c.dom.HTMLElement
-import org.w3c.dom.HTMLTextAreaElement
 
 @Composable
 fun TryLyngPage() {
@@ -34,7 +30,6 @@ fun TryLyngPage() {
             """
             // Welcome to Lyng! Edit and run.
             // Try changing the data and press Ctrl+Enter or click Run.
-            import lyng.stdlib
 
             val data = 1..5
             val evens = data.filter { it % 2 == 0 }.map { it * it }
@@ -142,7 +137,14 @@ fun TryLyngPage() {
             EditorWithOverlay(
                 code = code,
                 setCode = { code = it },
-                onRun = { runCode() }
+                onKeyDown = { ev ->
+                    val key = ev.key
+                    val ctrlOrMeta = ev.ctrlKey || ev.metaKey
+                    if (ctrlOrMeta && key.lowercase() == "enter") {
+                        ev.preventDefault()
+                        runCode()
+                    }
+                }
             )
         }
 
@@ -210,458 +212,3 @@ fun TryLyngPage() {
         }
     }
 }
-
-@Composable
-private fun EditorWithOverlay(
-    code: String,
-    setCode: (String) -> Unit,
-    onRun: () -> Unit,
-    tabSize: Int = 4,
-) {
-    var overlayEl by remember { mutableStateOf<HTMLElement?>(null) }
-    var taEl by remember { mutableStateOf<HTMLTextAreaElement?>(null) }
-    var lastGoodHtml by remember { mutableStateOf<String?>(null) }
-    var lastGoodText by remember { mutableStateOf<String?>(null) }
-    var pendingSelStart by remember { mutableStateOf<Int?>(null) }
-    var pendingSelEnd by remember { mutableStateOf<Int?>(null) }
-    var pendingScrollTop by remember { mutableStateOf<Double?>(null) }
-    var pendingScrollLeft by remember { mutableStateOf<Double?>(null) }
-
-    // Update overlay HTML whenever code changes
-    LaunchedEffect(code) {
-        // Insert highlighted spans directly without <pre><code> wrappers to avoid
-        // external CSS (e.g., docs markdown styles) altering font-size/line-height
-        // and causing caret drift.
-        fun htmlEscape(s: String): String = buildString(s.length) {
-            for (ch in s) when (ch) {
-                '<' -> append("&lt;")
-                '>' -> append("&gt;")
-                '&' -> append("&amp;")
-                '"' -> append("&quot;")
-                '\'' -> append("&#39;")
-                else -> append(ch)
-            }
-        }
-
-        fun trimHtmlToTextPrefix(html: String, prefixChars: Int): String {
-            if (prefixChars <= 0) return ""
-            var i = 0
-            var textCount = 0
-            val n = html.length
-            val out = StringBuilder(prefixChars + 64)
-            // Track open span tags to close them at the end
-            val stack = mutableListOf<String>() // holds closing tags like "</span>"
-            while (i < n && textCount < prefixChars) {
-                val ch = html[i]
-                if (ch == '<') {
-                    // Copy the whole tag
-                    val close = html.indexOf('>', i)
-                    if (close == -1) break
-                    val tag = html.substring(i, close + 1)
-                    out.append(tag)
-                    // Track span openings/closings
-                    val tagLower = tag.lowercase()
-                    if (tagLower.startsWith("<span")) {
-                        stack.add("</span>")
-                    } else if (tagLower.startsWith("</span")) {
-                        if (stack.isNotEmpty()) stack.removeAt(stack.lastIndex)
-                    }
-                    i = close + 1
-                } else if (ch == '&') {
-                    // entity counts as one text char
-                    val semi = html.indexOf(';', i + 1).let { if (it == -1) n - 1 else it }
-                    val entity = html.substring(i, semi + 1)
-                    out.append(entity)
-                    textCount += 1
-                    i = semi + 1
-                } else {
-                    out.append(ch)
-                    textCount += 1
-                    i += 1
-                }
-            }
-            // Close any open spans
-            for (j in stack.size - 1 downTo 0) out.append(stack[j])
-            return out.toString()
-        }
-
-        fun appendSentinel(html: String): String =
-        // Append a zero-width space sentinel to keep the last line box from collapsing
-        // in some browsers, which can otherwise cause caret size/position glitches
-            // when the caret is at end-of-line.
-            html + "<span data-sentinel=\"1\">&#8203;</span>"
-
-        try {
-            val html = SiteHighlight.renderHtml(code)
-            overlayEl?.innerHTML = appendSentinel(html)
-            lastGoodHtml = html
-            lastGoodText = code
-        } catch (_: Throwable) {
-            // Highlighter failed (e.g., user is typing an unterminated string).
-            // Preserve the last good highlighting for the common prefix, and render the rest as neutral text.
-            val prevHtml = lastGoodHtml
-            val prevText = lastGoodText
-            if (prevHtml != null && prevText != null) {
-                // Find common prefix length in characters between prevText and current code
-                val max = minOf(prevText.length, code.length)
-                var k = 0
-                while (k < max && prevText[k] == code[k]) k++
-                val prefixLen = k
-                val trimmed = trimHtmlToTextPrefix(prevHtml, prefixLen)
-                val tail = code.substring(prefixLen)
-                val combined = trimmed + htmlEscape(tail)
-                overlayEl?.innerHTML = appendSentinel(combined)
-                // Do NOT update lastGoodHtml/Text here; wait for the next successful highlight
-            } else {
-                // No previous highlight available; show plain neutral text so it stays visible
-                overlayEl?.innerHTML = appendSentinel(htmlEscape(code))
-            }
-        }
-
-        // keep overlay scroll aligned with textarea after re-render
-        val st = pendingScrollTop ?: (taEl?.scrollTop ?: 0.0)
-        val sl = pendingScrollLeft ?: (taEl?.scrollLeft ?: 0.0)
-        overlayEl?.scrollTop = st
-        overlayEl?.scrollLeft = sl
-
-        // If we have a pending selection update (from a key handler), apply it after the
-        // value has been reconciled in the DOM. Double rAF to ensure paint is ready.
-        val ps = pendingSelStart
-        val pe = pendingSelEnd
-        if (ps != null && pe != null) {
-            window.requestAnimationFrame {
-                window.requestAnimationFrame {
-                    val ta = taEl
-                    if (ta != null) {
-                        val s = ps.coerceIn(0, ta.value.length)
-                        val e = pe.coerceIn(0, ta.value.length)
-                        ta.selectionStart = s
-                        ta.selectionEnd = e
-                        // restore scroll as well
-                        if (pendingScrollTop != null) ta.scrollTop = pendingScrollTop!!
-                        if (pendingScrollLeft != null) ta.scrollLeft = pendingScrollLeft!!
-                    }
-                    pendingSelStart = null
-                    pendingSelEnd = null
-                    pendingScrollTop = null
-                    pendingScrollLeft = null
-                }
-            }
-        }
-    }
-
-    // helper: set caret/selection safely
-    fun setSelection(start: Int, end: Int = start) {
-        val ta = taEl ?: return
-        val s = start.coerceIn(0, (ta.value.length))
-        val e = end.coerceIn(0, (ta.value.length))
-        // Defer to next animation frame to avoid Compose re-render race
-        window.requestAnimationFrame {
-            ta.selectionStart = s
-            ta.selectionEnd = e
-        }
-    }
-
-    // Ensure overlay typography matches textarea to avoid shifted copies
-    LaunchedEffect(taEl, overlayEl) {
-        try {
-            val ta = taEl ?: return@LaunchedEffect
-            val ov = overlayEl ?: return@LaunchedEffect
-            val cs = window.getComputedStyle(ta)
-
-            // Resolve a concrete pixel line-height; some browsers return "normal" or unitless
-            fun ensurePxLineHeight(): String {
-                val lh = cs.lineHeight ?: ""
-                if (lh.endsWith("px")) return lh
-                // Measure using an off-screen probe with identical typography
-                val doc = ta.ownerDocument
-                val probe = doc?.createElement("span")?.unsafeCast<HTMLElement>()
-                if (probe != null) {
-                    probe.textContent = "M"
-                    val fw = try {
-                        (cs.asDynamic().fontWeight as? String) ?: cs.getPropertyValue("font-weight")
-                    } catch (_: Throwable) {
-                        null
-                    }
-                    val fs = try {
-                        (cs.asDynamic().fontStyle as? String) ?: cs.getPropertyValue("font-style")
-                    } catch (_: Throwable) {
-                        null
-                    }
-                    probe.setAttribute(
-                        "style",
-                        buildString {
-                            append("position:absolute; visibility:hidden; white-space:nowrap;")
-                            append(" font-family:").append(cs.fontFamily).append(';')
-                            append(" font-size:").append(cs.fontSize).append(';')
-                            if (!fw.isNullOrBlank()) append(" font-weight:").append(fw).append(';')
-                            if (!fs.isNullOrBlank()) append(" font-style:").append(fs).append(';')
-                            append(" line-height: normal;")
-                        }
-                    )
-                    doc.body?.appendChild(probe)
-                    val h = probe.getBoundingClientRect().height
-                    doc.body?.removeChild(probe)
-                    if (h > 0) return "${'$'}hpx"
-                }
-                // Fallback heuristic: 1.2 * font-size
-                val fsPx = cs.fontSize.takeIf { it.endsWith("px") }?.removeSuffix("px")?.toDoubleOrNull()
-                val approx = if (fsPx != null) fsPx * 1.2 else 16.0 * 1.2
-                return "${'$'}{approx}px"
-            }
-
-            val lineHeightPx = ensurePxLineHeight()
-            // copy key properties
-            val style = buildString {
-                append("position:absolute; inset:0; overflow:auto; pointer-events:none;")
-                append(" box-sizing:border-box; white-space: pre-wrap; word-wrap: break-word; tab-size:")
-                append(tabSize)
-                append(";")
-                // Typography
-                append("font-family:").append(cs.fontFamily).append(";")
-                append("font-size:").append(cs.fontSize).append(";")
-                append("line-height:").append(lineHeightPx).append(";")
-                append("letter-spacing:").append(cs.letterSpacing).append(";")
-                // Try to mirror weight and style to eliminate metric differences
-                val fw = try {
-                    (cs.asDynamic().fontWeight as? String) ?: cs.getPropertyValue("font-weight")
-                } catch (_: Throwable) {
-                    null
-                }
-                if (!fw.isNullOrBlank()) append("font-weight:").append(fw).append(";")
-                val fs = try {
-                    (cs.asDynamic().fontStyle as? String) ?: cs.getPropertyValue("font-style")
-                } catch (_: Throwable) {
-                    null
-                }
-                if (!fs.isNullOrBlank()) append("font-style:").append(fs).append(";")
-                // Disable ligatures in overlay to keep glyph advances identical to textarea
-                append("font-variant-ligatures:none;")
-                append("-webkit-font-smoothing:antialiased;")
-                append("text-rendering:optimizeSpeed;")
-                // Ensure overlay text is visible even when we render plain text (fallback)
-                append("color: var(--bs-body-color);")
-                // Padding to match form-control
-                append("padding-top:").append(cs.paddingTop).append(";")
-                append("padding-right:").append(cs.paddingRight).append(";")
-                append("padding-bottom:").append(cs.paddingBottom).append(";")
-                append("padding-left:").append(cs.paddingLeft).append(";")
-            }
-            ov.setAttribute("style", style)
-            // Also enforce the same concrete line-height on the textarea to keep caret metrics stable
-            try {
-                val existing = ta.getAttribute("style") ?: ""
-                if (!existing.contains("line-height")) {
-                    ta.setAttribute("style", existing + " line-height: " + lineHeightPx + ";")
-                }
-            } catch (_: Throwable) {
-            }
-        } catch (_: Throwable) {
-        }
-    }
-
-    // container
-    Div({
-        attr("style", "position: relative;")
-    }) {
-        // Highlight overlay below textarea
-        Div({
-            classes("font-monospace")
-            // Basic defaults; refined with computed textarea styles in LaunchedEffect above
-            attr(
-                "style",
-                buildString {
-                    append("position:absolute; inset:0; overflow:auto; pointer-events:none; box-sizing:border-box;")
-                    append(" white-space: pre-wrap; word-wrap: break-word; tab-size:")
-                    append(tabSize)
-                    append("; margin:0; font-variant-ligatures:none;")
-                }
-            )
-            ref {
-                overlayEl = it
-                onDispose { if (overlayEl === it) overlayEl = null }
-            }
-        }) {}
-
-        // Textarea on top
-        TextArea(value = code, attrs = {
-            classes("form-control", "font-monospace")
-            attr(
-                "style",
-                // Make text transparent to avoid double rendering, keep caret visible
-                "min-height: 220px; background: transparent; position: relative; z-index: 1; tab-size:${tabSize}; color: transparent; -webkit-text-fill-color: transparent; caret-color: var(--bs-body-color); font-variant-ligatures: none;"
-            )
-            // Turn off spellcheck and auto-correct features
-            attr("spellcheck", "false")
-            attr("autocorrect", "off")
-            attr("autocapitalize", "off")
-            attr("autocomplete", "off")
-            placeholder("Write some Lyng code…")
-            ref {
-                taEl = it
-                onDispose { if (taEl === it) taEl = null }
-            }
-            onMouseDown {
-                // Clear any pending programmatic selection; rely on the browser's placement
-                pendingSelStart = null
-                pendingSelEnd = null
-                pendingScrollTop = null
-                pendingScrollLeft = null
-            }
-            onClick {
-                // Keep overlay scroll in sync after pointer placement
-                val st = taEl?.scrollTop ?: 0.0
-                val sl = taEl?.scrollLeft ?: 0.0
-                overlayEl?.scrollTop = st
-                overlayEl?.scrollLeft = sl
-            }
-            onScroll {
-                // mirror scroll positions
-                val st = taEl?.scrollTop ?: 0.0
-                val sl = taEl?.scrollLeft ?: 0.0
-                overlayEl?.scrollTop = st
-                overlayEl?.scrollLeft = sl
-            }
-            onInput { ev -> setCode(ev.value) }
-            onKeyDown { ev ->
-                val ctrlEnter = (ev.ctrlKey || ev.metaKey) && ev.key == "Enter"
-                if (ctrlEnter) {
-                    ev.preventDefault()
-                    onRun()
-                    return@onKeyDown
-                }
-
-                val ta = ev.target.unsafeCast<HTMLTextAreaElement>()
-                val start = ta.selectionStart ?: 0
-                val end = ta.selectionEnd ?: 0
-                val savedScrollTop = ta.scrollTop
-                val savedScrollLeft = ta.scrollLeft
-
-                fun currentLineStartIndex(text: String, i: Int): Int {
-                    val nl = text.lastIndexOf('\n', startIndex = (i - 1).coerceAtLeast(0))
-                    return if (nl == -1) 0 else nl + 1
-                }
-
-                when (ev.key) {
-                    "Tab" -> {
-                        ev.preventDefault()
-                        // Shift+Tab -> outdent
-                        if (ev.shiftKey) {
-                            val text = code
-                            val regionStart = currentLineStartIndex(text, start)
-                            val regionEnd = if (start == end) {
-                                text.indexOf('\n', startIndex = start).let { if (it == -1) text.length else it }
-                            } else {
-                                text.indexOf('\n', startIndex = end).let { if (it == -1) text.length else it }
-                            }
-                            val region = text.substring(regionStart, regionEnd)
-                            val lines = region.split("\n")
-                            var removedFirst = 0
-                            var totalRemoved = 0
-                            val outdented = lines.mapIndexed { idx, line ->
-                                val toRemove = when {
-                                    line.startsWith("\t") -> 1
-                                    else -> line.take(tabSize).takeWhile { it == ' ' }.length
-                                }
-                                if (idx == 0) removedFirst = toRemove
-                                totalRemoved += toRemove
-                                line.drop(toRemove)
-                            }.joinToString("\n")
-                            val newCode = text.substring(0, regionStart) + outdented + text.substring(regionEnd)
-                            val newStart = (start - removedFirst).coerceAtLeast(regionStart)
-                            val newEnd = (end - totalRemoved).coerceAtLeast(newStart)
-                            pendingSelStart = newStart
-                            pendingSelEnd = newEnd
-                            pendingScrollTop = savedScrollTop
-                            pendingScrollLeft = savedScrollLeft
-                            setCode(newCode)
-                        } else {
-                            val before = code.substring(0, start)
-                            val after = code.substring(end)
-                            if (start != end) {
-                                // Indent selected lines
-                                val regionStart = currentLineStartIndex(code, start)
-                                val regionEnd =
-                                    code.indexOf('\n', startIndex = end).let { if (it == -1) code.length else it }
-                                val region = code.substring(regionStart, regionEnd)
-                                val lines = region.split("\n")
-                                val indentStr = " ".repeat(tabSize)
-                                val indented = lines.joinToString("\n") { line -> indentStr + line }
-                                val newCode = code.substring(0, regionStart) + indented + code.substring(regionEnd)
-                                val delta = tabSize * lines.size
-                                val newStart = start + tabSize
-                                val newEnd = end + delta
-                                pendingSelStart = newStart
-                                pendingSelEnd = newEnd
-                                pendingScrollTop = savedScrollTop
-                                pendingScrollLeft = savedScrollLeft
-                                setCode(newCode)
-                            } else {
-                                // Insert spaces to next tab stop
-                                val col = run {
-                                    val lastNl = before.lastIndexOf('\n')
-                                    val lineStart = if (lastNl == -1) 0 else lastNl + 1
-                                    start - lineStart
-                                }
-                                val toAdd = tabSize - (col % tabSize)
-                                val spaces = " ".repeat(toAdd)
-                                val newCode = before + spaces + after
-                                val newPos = start + spaces.length
-                                pendingSelStart = newPos
-                                pendingSelEnd = newPos
-                                pendingScrollTop = savedScrollTop
-                                pendingScrollLeft = savedScrollLeft
-                                setCode(newCode)
-                            }
-                        }
-                    }
-
-                    "Enter" -> {
-                        ev.preventDefault()
-                        val before = code.substring(0, start)
-                        val after = code.substring(end)
-                        val lineStart = currentLineStartIndex(code, start)
-                        val currentLine = code.substring(lineStart, start)
-                        val indent = currentLine.takeWhile { it == ' ' || it == '\t' }
-                        // simple brace-aware heuristic: add extra indent if previous non-space ends with '{'
-                        val trimmed = currentLine.trimEnd()
-                        val extra = if (trimmed.endsWith("{")) " ".repeat(tabSize) else ""
-                        val insertion = "\n" + indent + extra
-                        val newCode = before + insertion + after
-                        val newPos = start + insertion.length
-                        pendingSelStart = newPos
-                        pendingSelEnd = newPos
-                        pendingScrollTop = savedScrollTop
-                        pendingScrollLeft = savedScrollLeft
-                        setCode(newCode)
-                    }
-
-                    "}" -> {
-                        // If the current line contains only indentation up to the caret,
-                        // outdent by one indent level (tab or up to tabSize spaces) before inserting '}'.
-                        val text = code
-                        val lineStart = currentLineStartIndex(text, start)
-                        val beforeCaret = text.substring(lineStart, start)
-                        val onlyIndentBeforeCaret = beforeCaret.all { it == ' ' || it == '\t' }
-                        if (onlyIndentBeforeCaret) {
-                            ev.preventDefault()
-                            val removeCount = when {
-                                beforeCaret.endsWith("\t") -> 1
-                                else -> beforeCaret.takeLast(tabSize).takeWhile { it == ' ' }.length
-                            }
-                            val newLinePrefix = if (removeCount > 0) beforeCaret.dropLast(removeCount) else beforeCaret
-                            val after = code.substring(end)
-                            val newCode = code.substring(0, lineStart) + newLinePrefix + "}" + after
-                            val newPos = lineStart + newLinePrefix.length + 1
-                            pendingSelStart = newPos
-                            pendingSelEnd = newPos
-                            pendingScrollTop = savedScrollTop
-                            pendingScrollLeft = savedScrollLeft
-                            setCode(newCode)
-                        }
-                    }
-                }
-            }
-        })
-    }
-}