Ampersand in standard generalized markup language

In SGML (standard generalized markup language) and its descendants, such as HTML (hypertext markup language) and XML (extensible markup language), the ampersand is used to begin the encoding that represents a special character (i.e., a character that is not included in the limited standard character set), and such encoding is terminated with a semicolon.

For example, the HTML encoding for the at symbol (@) so that it will render correctly in a web browser is @, and the encoding for the copyright symbol (©) is ©. The ampersand can be encoded with a choice of & and &#amp;.