When you open a document, Dreamweaver fixes (or rewrites) certain kinds of technically illegal code, depending on which code rewriting preferences you specify. These preferences have no effect when you edit HTML or scripts in Code view.
If you disable the rewriting options, Dreamweaver displays invalid-markup items in the Document window for HTML that it would have rewritten.
The Code Rewriting preferences appear.
For more information, see Setting the code rewriting preference options.