C.1. ASCII Character SetHTML and XHTML documents use the standard 7-bit ASCII character set in their source. The first 31 characters in ASCII (not listed) are such device controls as backspace () and carriage return ( ) and are not appropriate for use in HTML documents. HTML 4.01 defines only four entities in this character range: less than (<, <), greater than (<, >), ampersand (&, &), and quotation mark (", "), that are necessary for escaping characters that may be interpreted as markup. XHTML also includes the ' entity that is included in every XML language. In XHTML documents, the ampersand symbol (&) must always be escaped in attribute values. For better compatibility with XML parsers, authors should use numerical character references instead of named character references for all other character entities.
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