All documents must begin with a Document Type Declaration <doctype> or DTD. The <doctype> informs a validator which version of (X)HTML to use when verifying a document's syntax.
![]() | <html lang="en"> <head> <title>Document missing doctype</title> </head> <body> </body> </html> |
![]() | <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> <html lang="en"> <head> <title>Document with valid doctype</title> </head> <body> </body> </html> |
Use a valid doctype.