- Enh #3723:`yii\filters\PageCache` now supports caching response headers as well as non-HTML response content (qiangxue)
- Enh #4710: Added `yii\web\AssetManager::appendTimestamp` to support cache busting for assets (qiangxue)
- Enh #5663: Added support for using `data-params` to specify additional form data to be submitted via the `data-method` approach (usualdesigner, qiangxue)
- Enh #5681: Allow customization of Menu::submenuTemplate in menu items (RobertBoes, otsec)
- Enh #6106: Added ability to specify `encode` for each item of `yii\widgets\Breadcrumbs` (samdark, aleksanderd)
- Enh #6361: Added `validateAttribute()` to `yii.activeForm.js` to support manually triggering data validation of an input (Alex-Code, qiang)
- Enh #6493: Added support for the `Access-Control-Expose-Headers` header by `yii\filters\Cors` (usualdesigner)