revert: remove syntax highlighting feature entirely

Syntax highlighting overlay approach proved too fragile:
- pixel alignment between textarea and overlay unreliable
- transparent textarea caused invisible content bugs
- dynamic gutter width positioning added complexity

Removed:
- _highlightEditor, _doHighlight, toggleSyntaxHighlight, _positionHighlightLayer
- highlightLayer DOM element creation
- .me-highlight-layer, .mh-*, .me-textarea-highlight CSS
- syntaxHighlight config option from DEFAULTS
- highlight toggle button from demo.html

Kept: Mermaid, fileSystem, preview links, all other v0.1.14 features

site/demo.html

@@ -68,7 +68,6 @@ body{font-family:-apple-system,BlinkMacSystemFont,"Segoe UI","PingFang SC","Micr
   <div class="spacer"></div>
   <button data-cmd="zen" title="Zen 专注模式">🧘 Zen</button>
   <button data-cmd="outline" title="切换大纲面板">📋 大纲</button>
-  <button data-cmd="highlight" title="切换语法高亮">🎨 高亮</button>
   <button data-cmd="wrap" title="切换自动换行">↩ 换行</button>
   <button data-cmd="toast" title="Toast 通知演示">💬 Toast</button>
   <button data-cmd="openFile" title="打开磁盘文件">📂 打开</button>
@@ -199,7 +198,6 @@ var editor=MeEditor.create('#editor',{
   value:demoMd,
   mode:'split',height:620,
   lineNumbers:true,autoBrackets:true,wordCount:true,
-  syntaxHighlight:true,
   theme:'auto',locale:'zh-CN',
   outline:false,
   plugins:['autoSave','exportTool','searchReplace','imagePaste','shortcutHelp','fileSystem'],
@@ -229,7 +227,6 @@ bar.addEventListener('click',function(e){
   if(cmd==='mode'){editor.setMode(btn.dataset.arg);updateModeBtns(btn.dataset.arg);}
   else if(cmd==='zen'){editor.toggleZen();btn.classList.toggle('on',editor.isZen());}
   else if(cmd==='outline'){toggleOutline(btn);}
-  else if(cmd==='highlight'){editor.toggleSyntaxHighlight();btn.classList.toggle('on',editor.config.syntaxHighlight);}
   else if(cmd==='wrap'){editor.toggleWordWrap();btn.classList.toggle('on',!editor.isWordWrap());}
   else if(cmd==='toast'){
     var types=['success','error','warning','info'];

src/constants.js

@@ -62,8 +62,6 @@ export const DEFAULTS = Object.freeze({
   wordWrap: true,
   // 最大字符数（v0.1.14，0=不限）
   maxLength: 0,
-  // 语法高亮编辑区（v0.1.14）
-  syntaxHighlight: true,
   // 主题：light / dark / auto / warm / 自定义
   theme: 'auto',
   // 国际化

src/core.js

@@ -6,7 +6,7 @@
  * v0.1.6: 插件依赖拓扑排序、实例 i18n、快捷键/工具栏定制、右键菜单、Toast
  * v0.1.7: 行号装订线、自动格式化、括号自动闭合、拖放、大纲面板
  * v0.1.12: 工具栏键盘导航、aria-live、Zen模式、滚动同步v2、WordWrap
- * v0.1.14: 语法高亮编辑区、图片上传钩子、预览链接拦截、Mermaid、文件存储
+ * v0.1.14: 预览链接拦截、Mermaid、文件存储
  */
 
 import { generateId, escapeHTML, isBrowser } from './utils.js';
@@ -115,7 +115,6 @@ class MarkdownEditor {
     this._zenMode = false;         // v0.1.12: Zen 模式
     this._wordWrap = true;         // v0.1.12: 自动换行
     this._syncing = false;         // 滚动同步锁
-    this._hlRaf = null;            // v0.1.14: 高亮节流
 
     // 渲染函数：自定义覆盖内置解析器
     this._renderFn = (typeof this.config.render === 'function') ? this.config.render : parseMarkdown;
@@ -217,12 +216,6 @@ class MarkdownEditor {
     if (!this.config.lineNumbers) gutter.style.display = 'none';
     editorInner.appendChild(gutter);
 
-    // 语法高亮叠加层（v0.1.14）
-    const highlightLayer = document.createElement('pre');
-    highlightLayer.className = 'me-highlight-layer';
-    highlightLayer.setAttribute('aria-hidden', 'true');
-    editorInner.appendChild(highlightLayer);
-
     const textarea = document.createElement('textarea');
     textarea.className = 'me-textarea';
     textarea.spellcheck = !!this.config.spellcheck;
@@ -230,12 +223,6 @@ class MarkdownEditor {
     textarea.style.tabSize = String(this.config.tabSize || 2);
     textarea.placeholder = this.config.placeholder || i18nT('placeholder');
     textarea.setAttribute('aria-label', i18nT('edit'));
-    if (this.config.syntaxHighlight) {
-      textarea.classList.add('me-textarea-highlight');
-    }
-    if (highlightLayer && !this.config.syntaxHighlight) {
-      highlightLayer.hidden = true;
-    }
     editorInner.appendChild(textarea);
 
     editorPane.appendChild(editorInner);
@@ -276,7 +263,6 @@ class MarkdownEditor {
     this.editorPane = editorPane;
     this.editorInner = editorInner;
     this.gutter = gutter;
-    this.highlightLayer = highlightLayer;
     this.previewPane = previewPane;
     this.dividerEl = divider;
     this.textarea = textarea;
@@ -343,7 +329,6 @@ class MarkdownEditor {
       this._updateWordCount();
       this._renderGutter();
       this._updateOutline();
-      this._highlightEditor();  // v0.1.14
       this._emit('input', this._value);
       this._emit('change', this._value);
       if (typeof this.config.onInput === 'function') {
@@ -1319,82 +1304,6 @@ class MarkdownEditor {
     requestAnimationFrame(() => { this._syncing = false; });
   }
 
-  // ============ 语法高亮编辑区（v0.1.14） ============
-
-  _highlightEditor() {
-    if (!this.highlightLayer || !this.config.syntaxHighlight) return;
-    // rAF 节流，避免高频更新
-    if (this._hlRaf) return;
-    this._hlRaf = requestAnimationFrame(() => {
-      this._hlRaf = null;
-      this._doHighlight();
-    });
-  }
-
-  _doHighlight() {
-    if (!this.highlightLayer || this.highlightLayer.hidden || this._mode === 'preview') return;
-    const text = this._value || '';
-    if (!text) { this.highlightLayer.innerHTML = ''; return; }
-    if (text.length > 50000) { this.highlightLayer.innerHTML = escapeHTML(text) + '\n'; return; }
-
-    let html = escapeHTML(text);
-    this._positionHighlightLayer();
-
-    // 正则按优先级：先匹配更具体的模式，避免被泛模式吞掉
-    // 1. 图片（先于链接）
-    html = html.replace(/!\[([^\]]*)\]\(([^)]+)\)/g, '<span class="mh-image">$&</span>');
-    // 2. 链接
-    html = html.replace(/\[([^\]]+)\]\(([^)]+)\)/g, '<span class="mh-link">$&</span>');
-    // 3. 行内代码（先于粗体/斜体，避免 `**` 被误匹配）
-    html = html.replace(/`([^`]+)`/g, '<span class="mh-code">$&</span>');
-    // 4. 粗体 **text** / __text__
-    html = html.replace(/(\*\*|__)(.+?)\1/g, '<span class="mh-bold">$&</span>');
-    // 5. 删除线
-    html = html.replace(/~~(.+?)~~/g, '<span class="mh-strike">$&</span>');
-    // 6. 斜体 *text* / _text_（在粗体之后，避免 ** 被拆成两个斜体）
-    html = html.replace(/(?<!\*)\*(?!\*)([^*\n]+?)\*(?!\*)/g, '<span class="mh-italic">$&</span>');
-    html = html.replace(/(?<!_)_(?!_)([^_\n]+?)_(?!_)/g, '<span class="mh-italic">$&</span>');
-    // 7. 标题（行级）
-    html = html.replace(/^(#{1,6})\s+(.+)$/gm, '<span class="mh-heading">$&</span>');
-    // 8. 列表标记
-    html = html.replace(/^(\s*[-*+]|\d+\.)\s/gm, '<span class="mh-list">$&</span>');
-    // 9. 引用
-    html = html.replace(/^(&gt;)\s?/gm, '<span class="mh-quote">$&</span>');
-    // 10. 水平线
-    html = html.replace(/^([-*_]{3,})\s*$/gm, '<span class="mh-hr">$&</span>');
-
-    this.highlightLayer.innerHTML = html + '\n';
-    // 同步滚动
-    if (this.textarea) this.highlightLayer.scrollTop = this.textarea.scrollTop;
-  }
-
-  /** 切换语法高亮（v0.1.14） */
-  toggleSyntaxHighlight() {
-    this.config.syntaxHighlight = !this.config.syntaxHighlight;
-    if (this.textarea) {
-      this.textarea.classList.toggle('me-textarea-highlight', this.config.syntaxHighlight);
-    }
-    if (this.highlightLayer) {
-      this.highlightLayer.hidden = !this.config.syntaxHighlight;
-    }
-    if (this.config.syntaxHighlight) {
-      this._positionHighlightLayer();
-      this._doHighlight();
-    }
-    return this;
-  }
-
-  _positionHighlightLayer() {
-    if (!this.highlightLayer) return;
-    // 动态设置左边距：有行号时对齐行号宽度，无行号时从 0 开始
-    if (this.gutter && this.config.lineNumbers && this.gutter.style.display !== 'none') {
-      const w = this.gutter.getBoundingClientRect().width;
-      this.highlightLayer.style.left = w + 'px';
-    } else {
-      this.highlightLayer.style.left = '0';
-    }
-  }
-
   _updateWordCount() {
     if (!this.config.wordCount || !this.statusEl) return;
     const text = this._value || '';
@@ -1781,7 +1690,6 @@ class MarkdownEditor {
     if (this._renderRaf) cancelAnimationFrame(this._renderRaf);
     if (this._historyTimer) clearTimeout(this._historyTimer);
     if (this._outlineTimer) clearTimeout(this._outlineTimer);
-    if (this._hlRaf) cancelAnimationFrame(this._hlRaf);
 
     this._cleanups.forEach((fn) => { try { fn(); } catch (_) {} });
     this._cleanups = [];

src/styles.js

@@ -132,31 +132,6 @@ const generateCSS = () => {
 
     /* ============ 编辑区内层（v0.1.7） ============ */
     .me-editor-inner { display: flex; height: 100%; overflow: hidden; position: relative; }
-    /* 语法高亮叠加层（v0.1.14） */
-    .me-highlight-layer {
-      position: absolute; top: 0; right: 0; bottom: 0;
-      padding: 16px 18px; margin: 0; border: 0; outline: 0; overflow: hidden;
-      font-family: var(--md-mono); font-size: 13.5px; line-height: 1.7;
-      white-space: pre-wrap; word-wrap: break-word;
-      pointer-events: none; background: var(--md-textarea-bg);
-      color: var(--md-text); z-index: 0;
-    }
-    /* textarea 在高亮模式下透明背景，露出下方高亮层 */
-    .me-textarea-highlight {
-      background: transparent !important;
-    }
-    /* 隐藏高亮层（语法高亮关闭时） */
-    .me-highlight-layer[hidden] { display: none; }
-    .mh-heading { color: var(--md-accent); font-weight: 700; }
-    .mh-bold { color: var(--md-text); font-weight: 700; }
-    .mh-italic { font-style: italic; }
-    .mh-strike { color: var(--md-muted); text-decoration: line-through; }
-    .mh-code { background: var(--md-code-bg); border-radius: 3px; padding: 0 2px; }
-    .mh-link { color: var(--md-accent); text-decoration: underline; }
-    .mh-image { color: #8b5cf6; }
-    .mh-list { color: var(--md-accent); font-weight: 600; }
-    .mh-quote { color: var(--md-muted); }
-    .mh-hr { color: var(--md-muted); }
     .me-gutter {
       flex: 0 0 auto;
       min-width: 36px;