First you should read more about how pasting works in RadEditor—http://docs.telerik.com/devtools/aspnet-ajax/controls/editor/managing-content/pasting-content/overview
. As you would see, it is the browser's responsibility to transform clipboard data from desktop apps to web apps. That said, you will see that using even a plain editable DOM element (like this one here—https://jsbin.com/godusoqela/edit?html,output
) the same results will happen when pasting from WordPad.
As for validation, there is no built-in approach to validate text while pasting and typing. This is a functionality that should be further handled by using the client-side event handlers—http://docs.telerik.com/devtools/aspnet-ajax/controls/editor/client-side-programming/events/overview
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and share your thoughts.