feat: #954 #940 增加frontMatter语法，并在frontMatter语法里支持了设置全局字体大小的能力

src/core/HooksConfig.js

@@ -49,6 +49,7 @@ import Suggester from './hooks/Suggester';
 import Ruby from './hooks/Ruby';
 import Panel from './hooks/Panel';
 import Detail from './hooks/Detail';
+import FrontMatter from './hooks/FrontMatter';
 /**
  * 引擎各语法的配置
  * 主要决定支持哪些语法，以及各语法的执行顺序
@@ -57,6 +58,7 @@ const hooksConfig = [
   // 段落级 Hook
   // 引擎会按当前排序顺序执行beforeMake、makeHtml方法
   // 引擎会按当前排序逆序执行afterMake方法
+  FrontMatter,
   CodeBlock,
   InlineCode,
   MathBlock,

src/core/hooks/FrontMatter.js

@@ -0,0 +1,51 @@
+/**
+ * Copyright (C) 2021 THL A29 Limited, a Tencent company.
+ *
+ * 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.
+ */
+import ParagraphBase from '@/core/ParagraphBase';
+import { compileRegExp } from '@/utils/regexp';
+
+export default class FrontMatter extends ParagraphBase {
+  static HOOK_NAME = 'frontMatter';
+
+  constructor(options) {
+    super({ needCache: true });
+  }
+
+  beforeMakeHtml(str) {
+    return str.replace(this.RULE.reg, (match, content) => {
+      const lineCount = match.match(/\n/g)?.length ?? 0;
+      const sign = `fontMatter${lineCount}`;
+      content.replace(/\n\s*(font-size|fontSize): ([0-9a-zA-Z]+)(\n|$)/, (match, m1, m2) => {
+        this.$engine.$cherry.previewer.getDom().style.fontSize = m2;
+        return match;
+      });
+      // 预判下是否为json格式，json格式就去掉换行，yaml格式就把换成换成分号
+      const dataContent = /^\s*{/.test(content) ? content.replace(/\n/g, '') : content.replace(/\n/g, ';');
+      const html = `<p data-sign="${sign}" data-type="frontMatter" data-lines="${lineCount}" data-content="${dataContent}"></p>`;
+      const placeHolder = this.pushCache(html, sign, lineCount);
+      return `${placeHolder}\n`;
+    });
+  }
+
+  makeHtml(str, sentenceMakeFunc) {
+    return str;
+  }
+
+  rule() {
+    const ret = { begin: '^\\s*-{3,}[^\\n]*\\n', end: '\\n-{3,}[^\\n]*\\n', content: '([\\s\\S]+?)' };
+    ret.reg = compileRegExp(ret, 'g', true);
+    return ret;
+  }
+}