Links and Webs - HTML and XHTML: The Definitive Guide - page 290

This URL actually references the resource named compute on the
www.calculator.com server and passes the string 3/4 to it, as delineated
by the question mark ( ? ). Presumably, the resource is a server-side pro-
gram that performs some arithmetic function on the passed value and
returns a result.

Unsafe characters are those that have no special meaning within the
URL but may have a special meaning in the context in which the URL is
written. For example, double quotes ( "" ) delimit URL attribute values in
tags. If you were to include a double quotation mark directly in a URL,
you would probably confuse the browser. Instead, you should encode
the double quotation mark as %22 to avoid any possible conflict.

Table 6-1 shows other reserved and unsafe characters that should al-
ways be encoded.

Table 6-1. Reserved and unsafe characters and their URL
encodings

Character Description Usage Encoding

; Semicolon Reserved %3B

/ Slash Reserved %2F

? Question mark Reserved %3F

: Colon Reserved %3A

@ At sign Reserved %40