Currently all major browsers offer their own built-in spellcheckers that perform spell check as you type out-of-the box in the editable elements: textareas, inputs, editable iframe and div elements. The content area of RadEditor is an editable IFRAME or DIV (when ContentAreaMode is set to DIV).
The required spell as you type feature is currently offered out-of-the box by all modern browsers Firefox, Chrome, Safari, Opera and the new Internet Explorer 10 (see this screenshot http://screencast.com/t/bbmhOHD0
the Telerik team
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