Clean Code Equals Strong Code

The Robust Principle asks developers of ICT to use clean HTML and CSS that can be parsed and processed in a way that won't break today, or in the future as new technologies come on the market. 

Guideline 4.1 Compatible

Maximize compatibility with current and future user agents, including assistive technologies.

When ICT is coded with integrity, it can withstand interaction with the widest set of technologies, user preferences, and modalities. This guideline asks developers to create clean code that leverages the standardized and compliant markup of current conventions.