In the Split View of iOS 11 you can drag sketches, doodles and even GIFs from an ordinary file right into your iMails and iMessages, or vice versa. In other words: any file is to use like a custom menu for personal emojis or stickers – self made or individual selected. See last page.
And yes: Instead of a file, you can open this website and drag my sketches into your Mails and Messages. Try it with the following sample (free for personal use).
In the iBook, however, there are hundreds of more examples, meant as role model for DIY stickers.
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