Fixing the mysterious “Element script is missing required attribute src” error

Suppose you're using the W3C validator to validate HTML5. Here's a sample document: <!doctype html> <html lang="en" xml:lang="en"> <head> <meta charset="utf-8" /> <title>Hello</title> <script type="text/javascript" charset="utf-8"> //<![CDATA[ var foo = 1; //]]> </script> </head> <body> </body> </html> Everything looks right, but you get this mysterious error: Line 6, Column 48: Element script is missing required […]