Tumblr.com provides a button on the post creation screen that allows you to view and edit the HTML source code for a post ... the gear-shaped "Preferences" icon at the top of the Tumblr.com ...

If you are comfortable with HTML, you can view and edit the code that the WYSIWYG attempts to hide. To view the HTML of the WYSIWYG you are working in, click on the <> icon. This will open a separate ...