Simple Code

• The WordPress editor allows you to switch between its WYSIWYG editor and its HTML editor on-the-fly. When you click "HTML" on a post, all of that post's coding is revealed -- to an extent. Even though, for example, WordPress allows you to define styles and attach stylesheets to blocks of text, these aren't always reflected in the code. A "<p>" code, for example, will be removed since WordPress assumes all text is body -- or paragraph text. This behavior is normal.
  
  

Complex Code

• While the WordPress editor strips basic code out of the HTML as part of its normal operation, most complex code should remain -- things like "iframe" and "embed" codes, for example. Even "table" codes should stay in your HTML, and if these bits of code are coming out when you toggle back to the visual editor, your WordPress install may have become corrupted. In this event, you may have to reinstall the WordPress software on your server.
  
  

Updates

• From time to time, the WordPress developers release updates to the core WordPress files. When you log in to the WordPress administrator area, click on "Updates" under the "Dashboard" heading on the left side menu. If a newer version of the core software exists, you should see a notice at the top of this screen. Click "Download" to upgrade your existing installation automatically. This process won't affect your content, but it will update the editor files and perhaps fix any errors with formatting and code.
  
  

Reinstall

• When core files become corrupted and your editor isn't working correctly, consider reinstalling the entire WordPress platform. This is an automated process that you control through the WordPress control panel. Log in to your site and click "Dashboard" and then "Updates." Click "Reinstall now" to replace the core files on your site with a fresh copy. The process doesn't affect your database so your content is untouched, but you can create a backup of your content through the "Tools" menu before proceeding.