About Character References
Characters not found in the normal alphanumeric character set, such as < and &, must be specified using Numeric Character References or predefined Character Entities. This process is known as escaping the character.
A Numeric Character Reference (NCR) refers to a character by its Unicode
code point in either decimal or hexadecimal form. Decimal character
references use the syntax
Hexadecimal values are indicated by an “x”:
&#xhhhh;. For example, the less-than (<)
character could be identified as
< (decimal) or
Character entities are abbreviated names for characters, such as
< for the less-than symbol.
Character entities are predefined in the HTML and XHTML DTDs as a convenience because they may be easier to remember.