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
    @_content_for ||= {}
    buf_was = @_out_buf
    @_out_buf = ''
    yield
    @_content_for[key] = @_out_buf
    @_out_buf = buf_was
  elsif @_content_for
    @_content_for[key]
  end
end