gistfile1.js

function pasteAsPlainTextWithNoFormatting() {   
    var cursorLocation = RTE.Cursor.get_range();
    var copiedData = window.self.clipboardData.getData('Text'); //Copy content from clipboard
    var copiedDataSpan = document.createElement('span');
    copiedDataSpan.setAttribute('id', 'copiedData');
    copiedDataSpan.innerText = copiedData; //add clipboard content to new span element
    cursorLocation.deleteContent();
    cursorLocation.insertBefore(copiedDataSpan); //add the content with the span element at the cursor location
    var rawContent = $ribbon('#copiedData').html(); //find that span 
    var cleanContent = rawContent.replace(/<[^>]*>/gi, ''); //remove all the formatting
    $ribbon('#copiedData').html(cleanContent);//add the content back 
    RTE.RteUtility.removeNodeAndKeepChildNodes(copiedDataSpan);//remove the span by keeping the data
    RTE.Cursor.update(); //update the cursor position
}