  Responsive Web Design (RWD) enables web applications to adapt to the
characteristics of different devices such as screen size which is important for
mobile browsing. Today, the only W3C standard to support this adaptability is
CSS media queries. However, using media queries it is impossible to create
applications in a modular way, because responsive elements then always depend
on the global context. Hence, responsive elements can only be reused if the
global context is exactly the same, severely limiting their reusability. This
makes it extremely challenging to develop large responsive applications,
because the lack of true modularity makes certain requirement changes either
impossible or expensive to realize.
  In this paper we extend RWD to also include responsive modules, i.e., modules
that adapt their design based on their local context independently of the
global context. We present the ELQ project which implements our approach. ELQ
is a novel implementation of so-called element queries which generalize media
queries. Importantly, our design conforms to existing web specifications,
enabling adoption on a large scale. ELQ is designed to be heavily extensible
using plugins. Experimental results show speed-ups of the core algorithms of up
to 37x compared to previous approaches.
