The fonts frequently used in hypertext markup language (HTML) documents are largely based on the original character set established under the American Standard for Information Interchange (ASCII). This means HTML ASCII is actually a series of special codes that can be inserted into an HTML document to display special characters that are either not available on a keyboard or that are control characters used in the markup language. The characters can be represented in different ways but commonly start with an ampersand symbol, followed by numbers or letters and completed with a semicolon. While it is not necessary to use any HTML ASCII characters, especially if they can be generated with a keyboard, it can sometimes be useful if a non-standard font is being used on a website. Even though an HTML ASCII character will accurately map to the correct character within a font, some documents use the Unicode® character set that can offer a much wider selection of characters.
The ASCII character set consists of 128 characters that can be held in 7 bits of a byte. An extended character set that uses the entire 8 bits of a byte includes an additional 128 characters. The characters include all the letters and numbers in the English language, as well as all the symbols that can be created on a standard English keyboard. In addition, several versions of commonly used letters with umlauts and other accents are available. Symbols for different national currencies, mathematical operations and frequently used business symbols also are within the basic ASCII set.
To use HTML ASCII in an HTML document, the character must be described in a special sequence known as an escape code. This begins with an ampersand followed by a pound and then the decimal number of the ASCII character, or a text representation of the character. One example is the symbol to denote a copyright. The copyright symbol is decimal number 169 in the ASCII character set, and can be written as the word copy in an HTML escape code. This means the character can either be included in an HTML document as © or as ©, with the semicolon at the end being necessary to complete the code.
One important use for HTML ASCII codes is to represent characters that are usually used as control characters within HTML. Characters such as the greater than and less than symbols are used to denote tags in HTML. To display one of these characters, the HTML ASCII escape code needs to be used instead of the typed symbol because, otherwise, the page code might become corrupt and cause the website not to be displayed properly.