When practical, adopt common conventions to minimize user confusion. When allotting space among elements competing for that space, user agents allot pixel and percentage lengths first, then divide up remaining available space among relative lengths. Length values are case-neutral. For information on specifying language codes in HTML, please consult the section on language codes . Whitespace is not allowed within the language-code.
Language codes are case-insensitive.
Names of character encodings are case-insensitive. User agents must follow the steps set out in the section on specifying character encodings in order to determine the character encoding of an external resource. 6.10 Single characters Certain attributes call for single character from the document character set . Exactly the components shown here must be present, with exactly this punctuation. 6.12 Link types Authors may use the following recognized link types, listed here with their conventional interpretations.