Here are some free WYSIWYG HTML Editor software and online tools. You can edit the output content and HTML source code and preview it.

The HTML is parsed, JavaScript is executed, and the result is the DOM. The content of a web page is not (just) source code, it’s the DOM. This makes it pretty important.

In previous versions of Microsoft Outlook (the classic app), you could view the HTML code of an email by opening the email, right-clicking on it, and selecting “View source” from the context menu.