@cwilcox808 @huijing Last year we moved the feature flags from a giant submenu to a new tab in Safari Settings — which makes it easier to find things quickly and reset back to default. The new design shipped in Safari 17.0. Patrick unveils it here: https://www.youtube.com/watch?v=14b6kdneO8Q

But feature flags were supported long before the Safari 17.0 redesign. Web developers could toggle feature flags from the Develop menu starting in Safari 10, in Sept 2016.

Before that, they were used by WebKit engineering.