code: def on_after_build_all(self, builder, **extra):
          
          # NOTE(vesuvium): compatibility for lektor 2.X and 3.X
          try:
              is_enabled = self.is_enabled(builder.build_flags)
          except AttributeError:
              is_enabled = self.is_enabled(builder.extra_flags)
  
          if not is_enabled:
              return
  
          reporter.report_generic('Starting HTML minification')
          for htmlfile in self.find_html_files(builder.destination_path):
              self.minify_file(htmlfile)
          reporter.report_generic('HTML minification finished')
docs: after-build-all lektor event