Use Tags and Smart Folders in Notes on your iPhone and iPad - Apple Support

Use tags to quickly categorize your notes so you can easily find them later. Just add one or more tags — like #work or #shopping — anywhere in any note. You can also use tags together with existing folders to search and filter your notes across multiple folders.

Use Smart Lists in Reminders on iPhone - Apple Support

Use Tags and Smart Folders in Notes on your iPhone and iPad - Apple Support

Draw or write in Notes on iPod touch - Apple Support (MY)

iCloud Notes

How To Quickly Organize iPhone Notes Using Tags & Smart Folders

Use Visual Look Up to identify objects in your photos and videos on iPhone - Apple Support

Get started with Notes on iPhone - Apple Support

Notes User Guide for Mac - Apple Support

Use Tags and Smart Folders in Notes on your iPhone and iPad - Apple Support

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Take notes on iPod touch - Apple Support (MY)