Create alternative syntax for frontmatter

packages/core/src/lib/markdown-it/index.ts

@@ -39,7 +39,8 @@ markdownIt.use(require('markdown-it-mark'))
   .use(require('./plugins/markdown-it-icons'))
   .use(require('./plugins/markdown-it-footnotes'))
   .use(require('./plugins/markdown-it-center-text'))
-  .use(require('./plugins/markdown-it-colour-text'));
+  .use(require('./plugins/markdown-it-colour-text'))
+  .use(require('./plugins/markdown-it-alt-frontmatter'));
 
 // fix table style
 markdownIt.renderer.rules.table_open = _.constant(

packages/core/src/lib/markdown-it/plugins/markdown-it-alt-frontmatter.js

@@ -0,0 +1,54 @@
+'use strict';
+
+// Process "---" => "<frontmatter>
+
+module.exports = function alt_frontmatter_plugin(md) {
+  function alt_frontmatter(state, startLine, endLine, silent) {
+    const fmSymbol = "---";
+    const keyValueRegex = new RegExp("^\\w+:\\s+.*");
+
+    let lineStart = state.bMarks[startLine] + state.tShift[startLine];
+    let lineEnd = state.eMarks[startLine];
+    let marker = state.src.slice(lineStart, lineEnd);
+    if (marker !== fmSymbol) { return false; }
+
+    let haveEndMarker = false;
+    let nextLine = startLine + 1;
+    for (; nextLine < endLine; nextLine++) {
+      lineStart = state.bMarks[nextLine] + state.tShift[nextLine];
+      lineEnd = state.eMarks[nextLine];
+
+      let currLine = state.src.slice(lineStart, lineEnd).trim();
+      if (currLine === fmSymbol) {
+        haveEndMarker = true;
+        break;
+      }
+      if (!(keyValueRegex.test(currLine) || currLine.length === 0)) {
+        // terminates if not key value or blank line.
+        return false;
+      }
+    }
+
+    if (!haveEndMarker) { return false; }
+    // If a fence has heading spaces, they should be removed from its inner block
+    let len = state.sCount[startLine];
+    state.line = nextLine + (haveEndMarker ? 1 : 0);
+
+    let token = state.push('alt_frontmatter', '', 0);
+    token.info = fmSymbol;
+    token.content = state.getLines(startLine + 1, nextLine, len, true);
+    token.markup = marker;
+    token.map = [ startLine, state.line ];
+    return true;
+  }
+
+  md.block.ruler.before('fence', 'alt_frontmatter', alt_frontmatter);
+  md.renderer.rules.alt_frontmatter = (tokens, idx, options, env, slf) => {
+    const token = tokens[idx];
+    if (token.type === 'alt_frontmatter' && token.info === '---') {
+      return '<frontmatter>\n' + token.content + '</frontmatter>\n';
+    }
+    return slf.renderToken(tokens, idx, options, env, slf);
+  };
+}
+