code: function performChange(content) {
    const exampleFile = ExampleFile.fromPath(this.file.path);
    const match = content.match(/<!---([\s\S]*)?--->/);
    if (!match) {
      return content;
    }
    gutil.log('changing', exampleFile.title);
    const frontmatter = JSON.parse(match[1]);
    const yaml = require('js-yaml');
    const yamlFrontmatter = `<!---
  
  ${yaml.safeDump(frontmatter)}
  --->
  ${content.substring(match[0].length)}`;
    /*
    if (!/<title>/.test(content)) {
      content = content.replace(/<meta charset="utf-8">/g,
          '<meta charset="utf-8">\n  <title>' + exampleFile.title() + '</title>');
    }
    */
    return yamlFrontmatter;
  }
docs: /* adds a title link to all sample files