&gt; I have no idea what motivates the inclusion of functionality that manipulates the clipboard in the browser.<p>I&#x27;m not sure, but I expect that it&#x27;s the same sort of thing that motivates the inclusion of the ability to enable page content obfuscation schemes that -say- scramble a page&#x27;s plaintext, but use CSS styles and JS voodoo to make it <i>appear</i> like the page contains only comprehensible text.<p>I expect that -when using such a scheme-, you&#x27;d need to be able to modify what is being tossed on to the clipboard, as -I expect that- the inbuilt selection tool will pick up your garbage data as well as the intended text. [0]<p>Edit: To be a little more practical, you could (for instance) use the ability to modify the contents of a clipboard to -say- create custom representations of your web application data formats and allow relatively easy transfer between instances of the software.<p>[0] Yes, I do recognize that allowing copy and paste kinda defeats the purpose of this scheme, but the scheme <i>is</i> something that I&#x27;ve seen in the wild.