For example, URI consumers should not treat %41 differently from A or %7E differently from ~, but some do. URIs that differ only by whether an unreserved character is percent-encoded or appears literally are equivalent by definition, but URI processors, in practice, may not always recognize this equivalence. This determination is dependent upon the rules established for reserved characters by individual URI schemes.Ĭharacters from the unreserved set never need to be percent-encoded. URIs that differ only by whether a reserved character is percent-encoded or appears literally are normally considered not equivalent (denoting the same resource) unless it can be determined that the reserved characters in question have no reserved purpose. The character does not need to be percent-encoded when it has no reserved purpose. In the ' query' component of a URI (the part after a ? character), for example, / is still considered a reserved character but it normally has no reserved purpose, unless a particular URI scheme says otherwise.

Reserved characters after characters that have no reserved purpose in a particular context may also be percent-encoded but are not semantically different from those that are not. If, according to a given URI scheme, / needs to be in a path segment, then the three characters %2F or %2f must be used in the segment instead of a raw /. The reserved character /, for example, if used in the 'path' component of a URI, has the special meaning of being a delimiter between path segments. (For a non-ASCII character, it is typically converted to its byte sequence in UTF-8, and then each byte value is represented as above.) The digits, preceded by a percent sign ( %) as an escape character, are then used in the URI in place of the reserved character. Percent-encoding a reserved character involves converting the character to its corresponding byte value in ASCII and then representing that value as a pair of hexadecimal digits (if there is a single hex digit, a leading zero are added). When a character from the reserved set (a 'reserved character') has a special meaning (a 'reserved purpose') in a certain context, and a URI scheme says that it is necessary to use that character for some other purpose, then the character must be percent-encoded. Other characters in a URI must be percent-encoded. RFC 3986 section 2.2 Reserved Characters (January 3986 section 2.3 Unreserved Characters (January 2005) The sets of reserved and unreserved characters and the circumstances under which certain reserved characters have special meaning have changed slightly with each revision of specifications that govern URIs and URI schemes. Using percent-encoding, reserved characters are represented using special character sequences. Unreserved characters have no such meanings. For example, forward slash characters are used to separate different parts of a URL (or more generally, a URI). Reserved characters are those characters that sometimes have special meaning. The characters allowed in a URI are either reserved or unreserved (or a percent character as part of a percent-encoding).

Percent-encoding in a URI Types of URI characters

2 The application/x-www-form-urlencoded type.

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