One of Slate's core principles is that, unlike most other editors, it does not prescribe a specific "schema" to the content you are editing. This means that Slate's core has no concept of "block quotes" or "bold formatting".
For the most part, this leads to increased flexbility without many downsides, but there are certain cases where you have to do a bit more work. Pasting is one of those cases.
Since Slate knows nothing about your domain, it can't know how to parse pasted HTML content (or other content). So, by default whenever a user pastes content into a Slate editor, it will parse it as plain text. If you want it to be smarter about pasted content, you need to override the insert_data command and deserialize the DataTransfer object's text/html data as you wish.
What browsers and devices does Slate support?
Slate's goal is to support all the modern browsers on both desktop and mobile devices.
Slate is in beta and is community-driven and so its support is not as robust as it could be.
On the desktop, it's currently tested against the latest few versions of Chrome, Edge, Firefox and Safari on desktops. And it does not work in Internet Explorer.
On mobile, iOS devices are supported but not regularly tested. Chrome on Android was until recently unsupported except for in older versions of Slate (0.47) but has recently been added. For clarity, due to the differences in Android's support of the beforeInput event, Android input uses compositions and mutations which is different from other browsers. This means that Android support progresses separately from other browsers and due to it being new, may have more bugs.
If you want to add or improve browser or device support, we'd love for you to submit a pull request! Or in the case of incompatible browsers, build a plugin.
For older browsers, such as IE11, a lot of the now standard native APIs aren't available. Slate's position on this is that it is up to the user to bring polyfills (like https://polyfill.io) when needed for things like el.closest, etc. Otherwise we'd have to bundle and maintain lots of polyfills that others may not even need in the first place. For clarity, Slate makes no guarantees that it will work with older browsers, even with polyfills and at present, there are still unresolved issues with IE11.