old_contents: # -*- coding: utf-8 -*-
  from cms.plugin_pool import plugin_pool
  from django.utils.translation import ugettext_lazy as _
  from cms.plugin_base import CMSPluginBase
  
  from layouter.forms import ContainerPluginForm
  from layouter.models import ContainerPlugin
  
  
  class ContainerCMSPlugin(CMSPluginBase):
      render_template = 'layouter/container.html'
      name = _('Layouting Row')
      model = ContainerPlugin
      allow_children = True
      form = ContainerPluginForm
      change_form_template = 'layouter/change_form.html'
  
      fieldsets = (
          (None, {
              'fields': ('container_type', 'margin')
          }),
          (_('Advanced'), {
              'classes': ('collapse',),
              'fields': ('css_classes',)
          })
      )
  
      def render(self, context, instance, placeholder):
          if instance.margin:
              context['width'] = 12 - 2 * instance.margin
          return super(ContainerCMSPlugin, self).render(context, instance, placeholder)
  
  plugin_pool.register_plugin(ContainerCMSPlugin)
  
new_contents: # -*- coding: utf-8 -*-
  from cms.plugin_pool import plugin_pool
  from django.utils.translation import ugettext_lazy as _
  from cms.plugin_base import CMSPluginBase
  
  from layouter.forms import ContainerPluginForm
  from layouter.models import ContainerPlugin
  
  
  class ContainerCMSPlugin(CMSPluginBase):
      render_template = 'layouter/container.html'
      name = _('Layouting Row')
      model = ContainerPlugin
      allow_children = True
      form = ContainerPluginForm
      change_form_template = 'layouter/change_form.html'
  
      fieldsets = (
          (None, {
              'fields': ('container_type', 'margin')
          }),
          (_('Advanced'), {
              'classes': ('collapse',),
              'fields': ('css_classes',)
          })
      )
  
      def render(self, context, instance, placeholder):
          context['width'] = 12 - 2 * instance.margin
          return super(ContainerCMSPlugin, self).render(context, instance, placeholder)
  
  plugin_pool.register_plugin(ContainerCMSPlugin)
  
subject: update margin calculation