Source mode is designed to handle complex html codes on an article, allowing to reduce the amount of unwanted code that is sometimes automatically added. Source mode is the best way to edit if you are using templates, or html tags such as <span>, <p>, and <div>. Click "Expand" to learn how to you can switch to this mode and make your code look cleaner.
Here are some useful tips:
When copy or pasting content, always use source mode!
When you see in the edit area of visual mode, it refers to a template, or content with code that is not supported or too complex for the visual editor to handle. In source mode you will see this content in full.
When you see in the edit area of visual mode, it refers to a comment. In source mode, you will see this content as <!-- -->.
MediaWiki has a special language called wikitext to make editing more easy. This language is supported in visual mode and will not break as easily as html.
Some html tags like <u> or <s> are supported in visual mode.
You can also enter source mode when creating or replying to threads in a forum, or when using a message wall by clicking underneath the edit area.