RFC=20
1738: Uniform Resource Locators (URL) specification=20
The specification for URLs (RFC 1738, =
Dec. '94)=20
poses a problem, in that it limits the use of allowed characters =
in URLs=20
to only a limited subset of the US-ASCII character set:=20
"...Only alphanumerics [0-9a-zA-Z], =
the=20
special characters "$-_.+!*'()," [not including the quotes - =
ed],=20
and reserved characters used for their reserved purposes may be =
used=20
unencoded within a URL." HTML, on the other hand, =
allows the=20
entire range of the ISO-885=
9-1=20
(ISO-Latin) character set to be used in documents - and HTML4 =
expands=20
the allowable range to include all of the Unicode=20
character set as well. In the case of non-ISO-8859-1 =
characters=20
(characters above FF hex/255 decimal in the Unicode set), they =
just can=20
not be used in URLs, because there is no safe way to specify =
character set=20
information in the URL content yet [RFC2396.]=20
URLs should be encoded everywhere in an HTML document that =
a URL=20
is referenced to import an object (A,=20
APP=
LET,=20
AREA<=
/A>,=20
BASE<=
/A>,=20
BG=
SOUND,=20
BODY<=
/A>,=20
EMBE=
D,=20
FORM<=
/A>,=20
FRAM=
E,=20
IFR=
AME,=20
ILA=
YER,=20
IMG<=
/A>,=20
IS=
INDEX,=20
=
INPUT,=20
LAYE=
R,=20
LINK<=
/A>,=20
OBJ=
ECT,=20
SCR=
IPT,=20
SOUN=
D,=20
TABL=
E,=20
TD,=20
TH,=20
and TR =
elements.)
What=20
characters need to be encoded and why?=20
| ASCII Control =
characters |
| |
Why: |
These characters are not printable. |
| Characters: |
Includes the ISO-885=
9-1=20
(ISO-Latin) character ranges 00-1F hex (0-31 decimal) =
and 7F=20
(127 decimal.) |
| Non-ASCII =
characters |
| |
Why: |
These are by definition not legal in URLs since they are =
not in=20
the ASCII set. |
| Characters: |
Includes the entire "top half" of the ISO-Lat=
in=20
set 80-FF hex (128-255 decimal.) |
| "Reserved =
characters" |
| |
Why: |
URLs use some characters for special use in defining their =
syntax. When these characters are not used in their special =
role=20
inside a URL, they need to be encoded. |
| Characters: |
| Character |
Code
Points
(Hex) |
Code
Points
(Dec) |
Dollar =
("$")
Ampersand=20
("&")
Plus ("+")
Comma=20
(",")
Forward slash/Virgule =
("/")
Colon=20
(":")
Semi-colon (";")
Equals=20
("=3D")
Question mark ("?")
'At' =
symbol=20
("@")
|
24
26
2B
2C
2F
3A
3B
3D
3F
40
| 36
38
43
44
47
58
59
61
63
64 | |
| "Unsafe =
characters" |
| |
Why: |
Some characters present the possibility of being=20
misunderstood within URLs for various reasons. These =
characters=20
should also always be encoded. |
| Characters: |
| Character |
Code
Points
(Hex) |
Code
Points
(Dec) |
Why encode? |
| Space |
20 |
32 |
Significant sequences of spaces may be =
lost in=20
some uses (especially multiple spaces) |
Quotation marks
'Less Than' symbol=20
("<")
'Greater Than' symbol (">") |
22
3C
3E |
34
60
62 |
These characters are often used to =
delimit URLs=20
in plain text. |
| 'Pound' character ("#") |
23 |
35 |
This is used in URLs to indicate where =
a=20
fragment identifier (bookmarks/anchors in HTML) =
begins. |
| Percent character ("%") |
25 |
37 |
This is used to URL encode/escape other =
characters, so it should itself also be =
encoded. |
Misc. =
characters:
Left=20
Curly Brace ("{")
Right Curly =
Brace=20
("}")
Vertical Bar/Pipe=20
("|")
Backslash=20
("\")
Caret=20
("^")
Tilde=20
("~")
Left Square Bracket=20
("[")
Right Square Bracket=20
("]")
Grave Accent ("`") |
7B
7D
7C
5C
5E
7E
5B
5D
60
123
125
124
92
94
126
91
93
96=
Some systems can possibly modify these=20
=
characters. | |
How are characters URL=20
encoded?=20
URL encoding of a character consists of a "%" =
symbol,=20
followed by the two-digit hexadecimal representation =
(case-insensitive) of=20
the ISO-Lat=
in=20
code point for the character.=20
- Example=20
-
- Space =3D decimal code point 32 in the ISO-Lat=
in=20
set.=20
- 32 decimal =3D 20 in hexadecimal=20
- The URL encoded representation will be "%20"=20
URL encoding converter=20
The box below allows you to convert content =
between its=20
unencoded and encoded forms. The initial input state is considered =
to be=20
"unencoded" (hit 'Convert' at the beginning to start in the =
encoded=20
state.) Further, to allow actual URLs to be encoded, this little =
converter=20
does not encode URL syntax characters (the ";", "/", "?", ":", =
"@",=20
"=3D", "#" and "&" characters)...if you also need =
to encode=20
these characters for any reason, see the "Reserved characters" =
table above=20
for the appropriate encoded values.
NOTE:
This converter uses the =
String.charCodeAt and=20
String.fromCharCode functions, which are only available in =
Javascript=20
version 1.2 or better, so it doesn't work in Opera 3.x and below, =
Netscape=20
3 and below, and IE 3 and below. Browser detection can be =
tiresome, so this will just fail in those browsers...you have been =
warned.=20
8-}
Browser=20
Peculiarities=20
- Internet Explorer is notoriously relaxed in its requirements =
for=20
encoding spaces in URLs. This tends to contribute to author =
sloppiness=20
in authoring URLs. Keep in mind that Netscape and Opera are much =
more=20
strict on this point, and spaces MUST be encoded if the =
URL is=20
to be considered to be correct.
| |