You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: pkg_file_analyser.rb
    path of file: ./repos/fastlane/fastlane_core/lib/fastlane_core
    
    the code of the file until where you have to start completion: require 'rexml/document'

require_relative 'helper'

module FastlaneCore
  class PkgFileAnalyser
    def self.fetch_app_identifier(path)
      xml = self.fetch_distribution_xml_file(path)
      return xml.elements['installer-gui-script/product'].attributes['id'] if xml
      return nil
    end

    # Fetches the app platform from the given pkg file.
    def self.fetch_app_platform(path)
      return "osx"
    end

    # Fetches the app version from the given pkg file.
    def sel
    
    def self.fetch_distribution_xml_file(path)
      Dir.mktmpdir do |dir|
        Helper.backticks("xar -C #{dir.shellescape} -xf #{path.shellescape}")

        Dir.foreach(dir) do |file|
          next unless file.include?('Distribution')

          begin
            content = File.open(File.join(dir, file))
            xml = REXML::Document.new(content)

            if xml.elements['installer-gui-script/product']
              return xml
            end
          rescue => ex
            UI.error(ex)
            UI.error("Error parsing *.pkg distribution xml #{File.join(dir, file)}")
          end
        end