code: function formatUserstyleCSSHeader(metadata) {
    const CSSmeta = JSON.parse(JSON.stringify(metadata)); // Local copy
  
    let header = '';
    header += '/* ==UserStyle==\n';
  
    let documentRules;
  
    Object.keys(userstyleSpec).forEach(prop => {
      if (_safePropGet(prop, CSSmeta) && _isAllowedCSSMetaProp(prop)) {
        if (prop === 'match') {
          documentRules = CSSmeta.match;
        } else {
          header += `@${_padPropName(prop, longestPropLength)} ${CSSmeta[prop]}\n`;
        }
      }
    });
  
    header += '==/UserStyle== */\n';
    if (documentRules && Object.keys(documentRules).length) {
      header += `@-moz-document\n  ${documentRules.join(',\n  ')}\n{\n`;
    }
    return header;
  }
docs: /*
  
  === setup user.css conversion ===