URIs, URNs, and SGML/XML public identifiers

When I was helping to develop the spec for URIs beginning urn:publicid:, which are the URI equivalent of SGML and XML public identifiers (either formal or not), I worked out this table of what was and was not legal according to publicid syntax, URN syntax, and URI syntax (I'm referencing an older RFC for URI syntax rather than the current one, because I used the older one and some terminology has changed.)

Character Name(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

What the codewords in the tables mean:

URN
	upper, lower, number, other	MAY be used without %-encoding.
	reserved	SHOULD NOT be used without %-encoding.
	excluded	MUST NOT be used without %-encoding.
URI
	lowalpha, upalpha, digits, mark	MAY be used without %-encoding; %-encoding MUST NOT affect semantics.
	reserved	MAY be used without %-encoding; %-encoding MAY affect semantics.
	space, delims, unwise	MUST NOT be used without %-encoding.
Status
	NORM	No encoding needed, can't be used as syntax.
	ENCODE	MUST be encoded (%-encoded or privately).
	AVAIL	Available for use as syntax character if literal use is %-encoded (AMPERSAND has no literal use).
	NULL	Not usable in pubids, included for completeness.