The Text editor allows you to write content in HTML. This editing mode is aimed at content editors who are comfortable working with HTML however, it may be useful when troubleshooting issues with content that does not appear as expected in the Visual editor.
Unfortunately, there is a lot of misinformation and it’s common to produce poor quality HTML code that may not work on all browsers or devices. You are encouraged to use only formatting options provided in the Visual toolbar and avoid writing your own HTML. If you need special formatting or layout, please contact the Web team. If you insist on writing code please learn standards-based best practice HTML.
Read about some other common errors.
Switching between Visual and Text view can cause some of your HTML tags to be lost, particularly if your code is not properly formatted. WordPress may strip it out.