# What's a prolog?

If you use Coda's code validation feature, you may be confused by errors about your document's "prolog".

"Prolog" is the official term for the section above the opening <html> tag, and only a few specific things are allowed there, such as a DOCTYPE declaration.

You may see this error if your document contains, for example, PHP code. The validator understands HTML syntax only, and may generate errors about the prolog if your document contains PHP or other non-HTML content at the top of the file.