Ubiquitous web applications (UWA) are required to be customizable, meaning their services need to be adaptable towards the context of use, e.g., user, location, time, and device. Considering UWA’s from a software engineering point of view, a systematic development on basis of models is crucial. Current web modeling languages, however, often disregard the crosscutting nature of customization potentially affecting all parts of a web application, and often mingle core and customization functionality. This leads to inefficient development processes, high maintenance overheads, and a low potential for reuse. We regard customization as a crosscutting concern in the sense of the aspect-oriented paradigm. As a proof of concept, we extend the prominent web modeling language WebML on basis of our reference architecture for aspect-oriented modeling. This allows for a clear separation between the core and customization functionality, and – as a spin-off – demonstrates how to bridge existing...