The URI encoding uses allows a few characters to be represented as-is: a through z, A through Z, 0-9, -, _, ., !, ~, *, ', ( and ). The remaining characters are encoded as %‹xx›, where ‹xx› is the two-character hex representation of the integer value of the character (where the mapping character–integer is determined by US-ASCII if the integer is less than 128).
The encoding, in line with RFC 2396’s recommendation, represents a character as-is, if possible. The decoding allows any characters to be represented by their hex values, and allows characters to be incorrectly represented as-is.
The rules for the application/x-www-form-urlencoded mimetype given in the HTML 4.0 spec are:
Control names and values are escaped. Space characters are replaced by +, and then reserved characters are escaped as described in RFC 1738, section 2.2: Non-alphanumeric characters are replaced by %‹xx› representing the ASCII code of the character. Line breaks are represented as CRLF pairs: %0D%0A. Note that RFC 2396 supersedes RFC 1738 [RFC1738].
The control names/values are listed in the order they appear in the document. The name is separated from the value by = and name/value pairs are separated from each other by either ; or &. When encoding, ; is used as the separator by default. When decoding, both ; and & are parsed as separators by default.
These rules differs slightly from the straight encoding in RFC 2396 in that + is allowed, and it represents a space. The net/uri-codec library follows this convention, encoding a space as + and decoding + as a space. In addtion, since there appear to be some brain-dead decoders on the web, the library also encodes !, ~, ', (, and ) using their hex representation, which is the same choice as made by the Java’s URLEncoder.
The current-alist-separator-mode parameter determines the separator used in the result.
The current-alist-separator-mode parameter determines the way that separators are parsed in the input.
|→ (one-of/c 'amp 'semi 'amp-or-semi 'semi-or-amp)|
|(current-alist-separator-mode mode) → void?|
|mode : (one-of/c 'amp 'semi 'amp-or-semi 'semi-or-amp)|
The default value is 'amp-or-semi, which means that both & and ; are treated as separators when parsing, and & is used as a separator when encoding. The other modes use/recognize only of the separators.