code: function _matchRegExp(val) {
    const expression = `${_escapeRegExp(val)}($|\\s|\\>|\\+|~|\\:|\\[)`;
    let expressionPrefix = '(^|\\s|\\>|\\+|~)';
    if (_isPlaceholder(val)) {
      // We just want to match an empty group here to preserve the arguments we
      // may be expecting in a RegExp match.
      expressionPrefix = '()';
    }
    return new RegExp(expressionPrefix + expression, 'g');
  }
docs: Private: creates a regular expression used to find rules that match inherit property.
  
  * `val` {String} inherit property to use to find selectors that contain it.
  
  Returns {RegExp} used for finding rules that match inherit property.