Single Page application

Reserved places for data_
in reserved rooms for sections,
hollow lonely page.

Observer design pattern

Box all that varies,
and to interface expose

avoid strongly coupled bodies,

in each-other sticking their nose

favor loosely coupled honeys,

for any change they predispose    
                        

for that  subscribe observer worries,
to be notified from their bros

keeping an eye on every wiz,
and every  update they disclose

          

UML class diagram of Observer pattern

Decorator design pattern

Open it to extension

but to modification close,

watch inheriting temptation,
for soon the tree explodes,

use rather wrapping decoration,
with few options compose,

anytime have a new creation,
as you wish as you choose.