Building in layers.
WHAT IT MEANS
Starting with content that works everywhere, then adding capability where it is supported.
WHAT THE LAYERS ARE
Markup delivering the content and function Styling improving presentation Scripts improving interaction
WHY IT MATTERS
Scripts fail: blocked, slow, erroring, or unsupported.
Connections fail partway. Older devices lack features.
WHAT THAT MEANS PRACTICALLY
A form should submit without scripts Navigation should work without scripts Content should be present in the markup
WHAT SCRIPTS SHOULD ADD
Validation before submission Updating without reloading Convenience and responsiveness
WHAT TO TEST
The site with scripts disabled.
WHAT THAT REVEALS
Whether anything essential depends on them.
WHAT TO DO ABOUT FEATURES NOT UNIVERSALLY SUPPORTED
Detect support, and provide an alternative or omit the enhancement.
WHAT NOT TO DO
Detect the browser and assume its capabilities.
WHY
Browsers change, and detection by name is always wrong eventually.
WHAT THIS MATTERS MOST FOR
Visitors on modest devices and unreliable connections.
