module Roda::RodaPlugins::ContentFor::InstanceMethods

def content_for(key, &block)

is no content stored with that key.
stored content with the given key, or return nil if there
under the given key. If called without a block, retrieve
If called with a block, store content enclosed by block 
def content_for(key, &block)
  if block
    outvar = render_opts[:template_opts][:outvar]
    buf_was = instance_variable_get(outvar)
    # clean the output buffer for ERB-based rendering systems
    instance_variable_set(outvar, '')
    @_content_for ||= {}
    @_content_for[key] = Tilt[render_opts[:engine]].new(&block).render
    instance_variable_set(outvar, buf_was)
  elsif @_content_for
    @_content_for[key]
  end
end