Module Js_clipboard

Wrapper around the browser interface to the system clipboard.

There are two standard ways of accessing the system clipboard from Javascript. This is because browsers are rightfully scared of privacy / cyber security implications of arbitrary webpages reading the clipboard without an explicit consent / knowlege of the user.

# 1. Synchronous Clipboard API

This API solves the consent / knowledge problem by replacing the event handlers that are run in response to the user pressing the default keyboard shortcuts for copy / paste AND requiring that all modification of the clipboard are done as part of that event handler.

For `copy` and `cut`, one can supply a custom content that will be put into the clipboard. For `paste`, one can run a custom action, preventing the default. At the time of writing, no permission restrictions apply to the Synchronous API.

https://www.w3.org/TR/clipboard-apis/#sync-clipboard-api

# 2. Asynchronous Clipboard API

This is the more powerful API. But it comes with more burden. Reading the clipboard and writing to it at arbitrary point in time, by calling specific Javascript functions. This works only on HTTPS websites and while the tab is focused. User must explicitly grant the permission for reading clipboard contents.

https://www.w3.org/TR/clipboard-apis/#async-clipboard-api

Most of the time you will want to use the Synchronous API, as it is easier to use, and more guaranteed to work.