HTML sometimes can be a mess. Froala WYSIWYG Editor has a reputation for creating a clean output, and it is sometimes used for this purpose only.
Cross browser and cross platform is a must and has been a core value for Froala from the beginning. We designed our WYSIWYG HTML editor to create W3C valid code.
We paste a lot from Microsoft Word or Excel, and the Froala Editor automatically cleans all the unnecessary code, making the HTML safe to be used on the web.