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I believe the WYSIWYG (What you see is what you get) editor was the greatest breakthroughs in Web 2.0 since it empowered individual with no knowledge in HTML to be able to publish content on the web. In the picture above you see some of the main features of Blogger's WYSIWYG editor.
Add a link (Hyper Link)
Add an image (Upload)
Add a video (Embed)