Features
- Addon-docs: Lazy load iframes (#12888)
Bug Fixes
- React: Allow Storybook packages to use React 17.x (#12908)
- React: Support JSX react transform introduced in 16.14.0 (#12899)
- Addon-viewport: Fill entire iframe width with drop shadow (#12870)
Maintenance
- CLI: Deprecate '--story-format=mdx' option (#12905)