Just the facts about public ids, URNs, and URIs

[John Cowan <jcowan@reutershealth.com>]

The following table shows which ASCII characters are legal as what
in XML public ids, RFC 2141 URNs, and RFC 2396 URIs.  See below
for explanations of terms.  Use a fixed font.

Character(s) 
	Pubid	URN		URI		Status
============ 
	=====	===		===		======

LATIN CAPITAL LETTER ?	yes	upper		lowalpha	NORM
LATIN SMALL LETTER ?	yes	lower		upalpha		NORM
DIGIT *			yes	number		digit 
	NORM
HYPHEN-MINUS 
	yes	other		mark		NORM
LEFT PARENTHESIS	yes	other		mark 
	NORM
RIGHT PARENTHESIS	yes	other		mark		NORM
FULL STOP		yes	other		mark 
	NORM
EXCLAMATION MARK	yes	other		mark		NORM
ASTERISK 
	yes	other		mark		NORM
LOW LINE		yes	other 
	mark		NORM
PLUS SIGN		yes	other		reserved 
AVAIL
COMMA 
		yes	other		reserved	AVAIL
COLON 
		yes	other		reserved	AVAIL
EQUALS SIGN		yes	other		reserved	AVAIL
SEMICOLON 
	yes	other		reserved	AVAIL
COMMERCIAL AT		yes	other		reserved	AVAIL
DOLLAR SIGN		yes	other		reserved	AVAIL
QUESTION MARK		yes	reserved	reserved	ENCODE
SOLIDUS 
		yes	reserved	reserved	ENCODE
NUMBER SIGN		yes	reserved	delims		ENCODE
PERCENT SIGN		yes	reserved	delims		ENCODE
SPACE 
		yes	excluded	space		ENCODE
APOSTROPHE 
	yes	excluded	mark		ENCODE
AMPERSAND 
	no	excluded	reserved	AVAIL
TILDE 
		no	excluded	mark		NULL
REVERSE SOLIDUS		no	excluded	delims		NULL
QUOTATION MARK		no	excluded	delims		NULL
LESS-THAN SIGN		no	excluded	delims		NULL
GREATER-THAN SIGN	no	excluded	delims		NULL
LEFT SQUARE BRACKET	no	excluded	unwise		NULL
RIGHT SQUARE BRACKET	no	excluded	unwise		NULL
CIRCUMFLEX		no	excluded	unwise		NULL
GRAVE ACCENT		no	excluded	unwise		NULL
LEFT CURLY BRACE	no	excluded	unwise		NULL
VERTICAL LINE		no	excluded	unwise		NULL
RIGHT CURLY BRACE	no	excluded	unwise		NULL


URN upper, lower, number, other: MAY be used without %-encoding.
URN reserved: SHOULD NOT be used without %-encoding.
URN excluded: MUST NOT be used without %-encoding.

URI lowalpha, upalpha, digits, mark: MAY be used without %-encoding;
	%-encoding MUST NOT affect semantics.
URI reserved: MAY be used without %-encoding;
	%-encoding MAY affect semantics.
URI space, delims, unwise: MUST NOT be used without %-encoding.

Status NORM: No encoding needed, can't be used as syntax.
Status ENCODE: MUST be encoded (%-encoded or privately).
Status AVAIL: Available for use as syntax character
	if literal use is %-encoded (AMPERSAND has no literal use).
Status NULL: Not usable in pubids, included for completeness.

-- 
There is / one art             || John Cowan <jcowan@reutershealth.com>
no more / no less              || http://www.reutershealth.com
to do / all things             || http://www.ccil.org/~cowan
with art- / lessness           \\ -- Piet Hein