RenderContext simplifies the implementation of template Nodes by providing a safe place to store state between invocations of a node's `render` method. The RenderContext also provides scoping rules that are more sensible for 'template local' variables. The render context stack is pushed before each template is rendered, creating a fresh scope with nothing in it. Name resolution fails if a variable is not found at the top of the RequestContext stack. Thus, variables are local to a specific template and don't affect the rendering of other templates as they would if they were stored in the normal template context.
This method overrides django.template.context.BaseContext.__contains__.
This method overrides django.template.context.BaseContext.__getitem__.