[1] Error levels:
- (missing): An error.
- [Q@en[m]]: A violation to [['''MUST''']]-level constraint.
- [Q@en[NC]]: A namespace constraint in XML Namespace
specifications.
- [Q@en[error]]: An error.
- [Q@en[s]]: A violation to [['''SHOULD''']]-level constraint.
- [Q@en[w]]: A warning (which has no influence to the conformance).
- [Q@en[unsupported]]: The checker does not support
the target so that it cannot be checked.

[2] Error types:
- [CODE(perl)@en[[[Whatpm::CacheManifest]]]]:
-- [Q@en[both in entries and whitelist]]: The IRI is contained
both in explicit or fallback entries and in online whitelist.
-- [Q@en[different scheme from manifest]]: The URI scheme of an
IRI reference is different from that of the manifest's URI.
-- [Q@en[different shp from manifest]]: The opportunistic
caching namespace has different scheme/host/port from
those of manifest's URI.
-- [Q@en[duplicate oc namespace]]: The opportunistic caching
namespace is already mapped to a fallback entry. 
-- [Q@en[manifest URI]]: The URI is same as the manifest's URI.
-- [Q@en[no fallback entry URI]]: The second IRI reference
is not contained in a data line in a [CODE@en[FALLBACK]] section.
-- [Q@en[not manifest]]: The given entity is not a cache manifest.
-- [Q@en[URI fragment not allowed]]: A fragment identifier is
contained in an IRI reference.
-- [Q@en[URI::syntax error:iriref3987]]: A string that is not
a syntactically valid [[RFC 3987]] IRI reference is specified
where an IRI reference is expected.
-- [Q@en[URI::[VAR@en[t]]]]:
A URI error with type [VAR@en[t]].
-- [Q@en[URI::[VAR@en[t]]:[VAR@en[i]]]]:
A URI error with type [VAR@en[t]] at the [VAR@en[i]][SUP@en[th]]
character.
- ContentChecker:
-- [Q@en[attribute missing:[VAR@en[n]]]]: The attribute
whose name is [VAR@en[n]] is not set to the element
while the definition of the element requires it.
--- might be a [CODE@en[s]]-level error.
-- [Q@en[attribute missing:data|type]]
-- [Q@en[attribute missing:href|target]]: Neither 
[CODE(HTMLa)@en[[[href]]]] nor [CODE(HTMLa)@en[[[target]]]]
attribute is set to a [CODE(HTMLe)@en[[[base]]]] element.
-- [Q@en[attribute missing:name|http-equiv]]
-- [Q@en[attribute missing:name|http-equiv|charset]]
-- [Q@en[attribute not allowed]]: The attribute is set
to an element but it is not allowed according to the
definition of it.
-- [Q@en[attribute not allowed:ismap]]: The [CODE(HTMLa)@en[[[ismap]]]]
attribute is set to an element but it is not allowed since
there is no ancestor [CODE(HTMLe)@en[[[a]]]] element whose
[CODE(HTMLa)@en[[[href]]]] attribute is set.
-- [Q@en[attribute not defined]]
-- [Q@en[basehref after URI attribute]]: There is a
[CODE(HTMLe)@en[[[base]]]] element with
[CODE(HTMLa)@en[[[href]]]] attribute and the element
is after an element with URI attribute in tree order.
-- [Q@en[basetarget after hyperlink]]: There is a
[CODE(HTMLe)@en[[[base]]]] element with
[CODE(HTMLa)@en[[[target]]]] attribute and the element
is after an element that defines a hyperlink in tree order.
-- [Q@en[boolean:invalid]]: It is a boolean attribute
but the specified value is not same as the attribute name.
-- [Q@en[character not allowed]]: The character is not 
allowed where it occurs.
-- [Q@en[character not allowed]]: A non-whitespace character
is not allowed in an empty element.
-- [Q@en[character not allowed:atom|TextConstruct]]: Characters
are not allowed in [[Atom]] Text construct with its
[CODE(XMLa)@en[[[type]]]] attribute set to [CODE(XML)@en[[[xhtml]]]].
-- [Q@en[character encoding:[VAR@en[c]]]]: Character encoding
[VAR@en[c]] is used.
--- With level [VAR@en[m]]: The character encoding is not allowed.
--- With level [VAR@en[s]]: The character encoding is not recommended.
--- With level [VAR@en[w]]: Use of another encoding is encouraged.
--- With level [VAR@en[unsupported]]: The document has no input
encoding information, therefore the conformance checker cannot check
the document against character encoding requirements.
-- [Q@en[charset:not preferred:[VAR[s]]]]: The charset value
[VAR@en[s]] is not a preferred MIME name.
-- [Q@en[charset:not registered:[VAR[s]]]]: The charset value
[VAR@en[s]] is not a registered IANA charset name.
-- [Q@en[charset:private:[VAR[s]]]]: The charset value 
[VAR@en[s]] is a private name.
-- [Q@en[charset:syntax error]]: The charset value is not syntactically
valid.
-- [Q@en[child element missing:[VAR@en[e]]]]: There must
be a child element [VAR@en[e]].
-- [Q@en[child element missing:td|th]]
-- [Q@en[coords:number:[VAR@en[n]]:[VAR@en[m]]]]: There are 
[VAR@en[m]] items in the coords value while
there should be [VAR@en[n]] items according to
the definition of it.
-- [Q@en[coords:number:even:[VAR@en[m]]]]: There are
[VAR@en[m]] items in the coords value while
there should be even number of items according to
the definition of it.
-- [Q@en[coords:number:''>''=[VAR@[n]]:[VAR@en[m]]]]: There are
[VAR@en[m]] items in the coords value while
there should be more than [VAR@en[m]] items according to
the definition of it.
-- [Q@en[coords:out of range:[VAR@en[i]]]]: The 
[VAR@en[i]][SUP@en[th]] value of the coords value is outside
of the range.
-- [Q@en[coords:syntax error]]: The specified value
is not a coords value.
-- [Q@en[dateortime:syntax error]] The specified value
is not a date or time value.
-- [Q@en[datetime:bad day]]: The day part of the date
is incorrect.
-- [Q@en[datetime:bad hour]]: The hour part of the time
is incorrect.
-- [Q@en[datetime:bad minute]]: The minute part pf the time
is incorrect.
-- [Q@en[datetime:bad month]]: The month part of the date
is incorrect.
-- [Q@en[datetime:bad second]]: The second part of the time
is incorrect.
-- [Q@en[datetime:bad timezone hour]]: The hour part
of the timezone is incorrect.
-- [Q@en[datetime:bad timezone minute]]: The minute part
of the timezone is incorrect.
-- [Q@en[datetime:syntax error]]: The datetime specification
has a syntax error.
-- [Q@en[deprecated:attr]]
-- [Q@en[deprecated:element]]
-- [Q@en[duplicate ID]]: The [CODE(SGML)@en[[[ID]]]]
has also been specified to another element.
-- [Q@en[duplicate token:[VAR@en[t]]]]: It is an attribute
defined as a list of values that does not allow duplication
but there are two [VAR@en[t]]s specified.
-- [Q@en[element missing:hn]]: The element should contain
at least one [CODE(HTMLe)@en[[[h[VAR@en[n]]]]]] element
in the content, but there is no such element.
-- [Q@en[element missing:atom|[VAR@en[e]]]]: The element
should contain at leat one [CODE(XMLe)@en[[VAR@en[e]]]]
element in the [[Atom]] namespace in the content,
but there is no such element.
-- [Q@en[element missing:atom|link|alternate]]: There must
be a child [[Atom]] [CODE(XMLe)@en[[[link]]]] element
with the [CODE(XMLa)@en[[[rel]]]] attribute set
to [CODE(XML)@en[[[alternate]]]].
-- [Q@en[element missing:atom|link|self]]: There must
be a child [[Atom]] [CODE(XMLe)@en[[[link]]]] element
with the [CODE(XMLa)@en[[[rel]]]] attribute set
to [CODE(XML)@en[[[self]]]].
-- [Q@en[element not allowed]]: The element is placed where
it is not allowed according to the definition of that
element.
-- [Q@en[element not allowed:area]]: An [CODE(HTMLe)@en[[[area]]]]
element must be a descendant of a [CODE(HTMLe)@en[[[map]]]] element.
-- [Q@en[element not allowed:atom|TextConstruct]]: Elements
other than a [CODE(HTMLe)@en[[[div]]]] element are not allowed in
[[Atom]] Text construct with its [CODE(XMLa)@en[[[type]]]] attribute
set to [CODE(XML)@en[[[xhtml]]]].
-- [Q@en[element not allowed:base]]: There must not be
more than one [CODE(HTMLe)@en[[[base]]]] per document.
-- [Q@en[element not allowed:details legend]]
-- [Q@en[element not allowed:empty]]: The element is not allowed
in an empty element.
-- [Q@en[element not allowed:figure legend]]
-- [Q@en[element not allowed:head noscript]]
-- [Q@en[element not allowed:head style]]: The [CODE(HTMLe)@en[[[style]]]]
element has [CODE(HTMLa)@en[[[scoped]]]] attribute specified.  However,
it is not allowed in a [CODE(HTMLe)@en[[[head]]]] element.
-- [Q@en[element not allowed:head title]]: There are more than
one [CODE(HTMLe)@en[[[title]]]] elements.
-- [Q@en[element not allowed:meta charset]]: The charset declaration
element must be the first element in the 
[CODE(HTMLe)@en[[[head]]]] element.
-- [Q@en[element not allowed:minus]]: The element is not allowed
because of one of ancestor elements.
-- [Q@en[element not allowed:phrasing]]: The element is not allowed
in phrasing content.
-- [Q@en[element not allowed:prose]]: The element is not allowed in
prose content.
-- [Q@en[element not allowed:prose style]]: The 
[CODE(HTMLe)@en[[[style]]]] element in prose content must be
placed before any other element and any text node other than
inter-element whitespace and must have its [CODE(HTMLa)@en[[[scoped]]]]
attribute specified.
-- [Q@en[element not allowed:root]]: The element is not allowed
as a root element, according to the knowledge of the
conformance checker.
-- [Q@en[element not allowed:root:xml]]: The element is not allowed
as the root element of an XML document, according to the 
knowledge of the conformance checker.
-- [Q@en[element not defined]]: The element is not defined by 
the specification of that namespace.
-- [Q@en[empty attribute value]]: The attribute value
is an empty string, which is not allowed.
-- [Q@en[enumerated:invalid]]: It is an enumerated
attribute attribute and the specified value is not
a known one.
-- [Q@en[enumerated:non-conforming]]: It is an 
enumerated attribute and the specified value is one
of known values, but it is not conforming.
-- [Q@en[float:out of range]]: The specified floating point number
is outside of the range.
-- [Q@en[float:syntax error]]: The specified value is not
a floating point number.
-- [Q@en[fragment points nothing]]: The fragment identifier points no part
in the document.
-- [Q@en[#idref:syntax error]]: The specified value is not
a hashed ID reference.
-- [Q@en[IMT:[VAR@en[t]]]]: An Internet Media Type 
error [VAR@en[t]].
-- [Q@en[IMT:composite]]: The specified value represents
a composite type.
-- [Q@en[IMT:syntax error]]: The specified value is not
an Internet Media Type.
-- [Q@en[in HTML:xml:lang]]: A [CODE(XMLa)@en[[[xml]]:[[lang]]]]
attribute is specified in HTML document.
-- [Q@en[in XML:charset]]: An HTML [CODE(HTMLe)@en[[[meta]]]]
[CODE(HTMLa)@en[[[charset]]]] declaration is found
in an XML document.
-- [Q@en[in XML:lang]]: An HTML [CODE(HTMLa)@en[[[lang]]]]
attribute is specified in XML document.
-- [Q@en[in XML:noscript]]: An HTML [CODE(HTMLe)@en[[[noscript]]]]
element is found in XML document.
-- [Q@en[in XML:xmlns]]: An [CODE(HTMLa)@en[[[xmlns]]]]
attribute in the [CODE(DOM)@en[[[null]]]] attribute
is found in an XML document.
-- [Q@en[integer:syntax error]]: The attribute value
is not an integer.
-- [Q@en[invalid attribute value]]: The value set to the
attribute is not allowed according to the definition of
that attribute.  (If more specific error type is available,
then that one is used instead.)
-- [Q@en[keyword:invalid]]: The specified value
is not a valid keyword.
-- [Q@en[language tag:syntax error]]: The specified value
is not a language tag.
-- [Q@en[link type:bad context:[VAR@en[t]]]]:
The link type [VAR@en[t]] is not allowed for the
element it is specified to.
-- [Q@en[link type:duplicate:[VAR@en[t]]]]:
The link type [VAR@en[t]] is so defined that
there must be at most one element with that link type.
However, there are more than two elements with
that link type.
-- [Q@en[link type:non-conforming:[VAR@en[t]]]]:
The link type [VAR@en[t]] is not conforming one.
-- [Q@en[link type:proposed:[VAR@en[t]]]]:
The link type [VAR@en[t]] is proposed but not yet
accepted.
-- [Q@en[meta content-type syntax error]]: The syntax of
the [CODE(HTMLa)@en[[[content]]]] attribute value for a
character encoding declaration with [CODE(HTMLa)@en[[[http-equiv]]]]
attribute is invalid.
-- [Q@en[mismatched charset name:[VAR@en[s]]:[VAR@en[t]]]]:
The document character encoding is [VAR@en[s]], while
the character encoding declaration states as [VAR@en[t]].
-- [Q@en[mode:syntax error]]: The specified mode is an empty string
or contains a space character.
-- [Q@en[nninteger:out of range]]: The specified
non-negative integer is outside of the range.
-- [Q@en[nninteger:syntax error]]: It is not a
non-negative integer.
-- [Q@en[no character encoding declaration:[VAR@en[c]]]]:
Neither transfer layer charset label nor character encoding declaration
is found.
-- [Q@en[no document element]]: There is no document element.
-- [Q@en[no header cell]]: A token in a [CODE(HTMLa)@en[[[headers]]]] attribute
does not identify a header cell in the same table.
-- [Q@en[no referenced map]]: There is no map with the 
specified ID.
-- [Q@en[no referenced menu]]: There is no menu with the
specified ID.
-- [Q@en[no significant content]]: There is no descendant node
that is a [CODE(DOMi)@en[[[Text]]]] but not a inter-element whitespace 
or that is an embedded content.
-- [Q@en[non ascii superset:[VAR@en[c]]]]: The character encoding 
of document is not a superset of [[US-ASCII]] for the purpose of 
character encoding detection and the document has no charset
label nor [CODE(charname)@en[[[BOM]]]].
-- [Q@en[not IMT]]: The specified value does not 
represent an Internet Media Type.
-- [Q@en[ps element missing:[VAR@en[e]]]]: There should
be an [VAR@en[e]] element before this element or character.
-- [Q@en[repeat:syntax error]]: The value of the [CODE(HTMLa)@en[[[repeat]]]]
attribute is neither a string [CODE(HTML)@en[[[template]]]] nor an integer.
-- [Q@en[Reserved Prefixes and Namespace Names:=xml]]:
A namespace constraint error.
-- [Q@en[Reserved Prefixes and Namespace Names:xmlns:xml=]]:
A namespace constraint error.
-- [Q@en[Reserved Prefixes and Namespace Names:xmlns:xmlns=]]:
A namespace constraint error.
-- [Q@en[Reserved Prefixes and Namespace Names:<xmlns:>]]:
A namespace constraint error.
-- [Q@en[selectors:[VAR@en[e]]]]: An selectors error with type
[VAR@en[e]].
-- [Q@en[space in ID]]: There is a space character in ID.
-- [Q@en[table:[VAR@en[t]]]]:
A table error with type [VAR@en[t]].
-- [Q@en[template:not template]]: The element pointed
by the [CODE(HTMLa)@en[[[template]]]] attribute is not a 
[CODE(HTMLe)@en[[[datetemplate]]]] element.
-- [Q@en[URI::[VAR@en[t]]]]:
A URI error with type [VAR@en[t]].
-- [Q@en[URI::[VAR@en[t]]:[VAR@en[i]]]]:
A URI error with type [VAR@en[t]] at the [VAR@en[i]][SUP@en[th]]
character.
-- [Q@en[URIs:[VAR@en[n]]::[VAR@en[t]]]]:
The attribute is defined as a list of URIs.
The [VAR@en[n]][SUP@en[th]] URI has an error with type
[VAR@en[t]].
-- [Q@en[URIs:[VAR@en[n]]::[VAR@en[t]]:[VAR@en[i]]]]:
The attribute is defined as a list of URIs.
The [VAR@en[n]][SUP@en[th]] URI has an error with type
[VAR@en[t]] at the [VAR@en[i]][SUP@en[th]] character.
-- [Q@en[window name:empty]]: An empty string is specified where a valid
browsing context name (or keyword) is expected.
-- [Q@en[window name:reserved]]: A reserved keyword is specified in
a [CODE(HTMLa)@en[[[target]]]] attribute or a keyword is specified in
a [CODE(HTMLa)@en[[[name]]]] attribute that defines the browsing context name.
- [CODE(perl)@en[[[Whatpm::CSS::Parser]]]]
-- [Q@en[at-rule not allowed:[VAR@en[keyword]]]]: 
A [CODE(CSS)[@[VAR@en[keyword]]]] rule appears where it is not allowed.
-- [Q@en[at-rule not supported]]: An unsupported at-rule appears.
-- [Q@en[at-rule syntax error:[VAR@en[keyword]]]]:
A [CODE(CSS)@en[@[VAR[keyword]]]] rule is syntactically invalid.
-- [Q@en[block not closed]]: A block is not closed before the
end of the style sheet.
-- [Q@en[duplication:[VAR@en[production]]]]: More than allowed number
of [CODE(CSS)@en[<[VAR@en[production]]>]] component is found.
-- [Q@en[no declaration block]]: No declaration block is found
before the end of the style sheet.
-- [Q@en[no property colon]]: No [CODE(charname)@en[[[COLON]]]] character
is found after a property name.
-- [Q@en[no property name]]: No property name is found in a
declaration.
-- [Q@en[no property semicolon]]: No [CODE(charname)@en[[[SEMICOLON]]]]
character is found after a property specification.
-- [Q@en[priority syntax error]]: A priority specification is
invalid.
-- [Q@en[property not supported]]: An unsupported CSS property appears.
-- [Q@en[syntax error:[VAR[production]]]]: A value whose syntax
is defined as [CODE(CSS)@en[<[VAR[production]]>]] is 
syntactically invalid.
-- [Q@en[uri not closed]]: A [CODE(CSS)@en[[[URI]]]] token is not
closed by optional [CODE(CSS)[[["]]]] followed by mandatory
[CODE(CSS)[[[)]]]].
- [CODE(perl)@en[[[Whatpm::CSS::SelectorsParser]]]]
-- [Q@en[namespace prefix:not declared]]
-- [Q@en[an+b not integer]]: A non-integer number is specified
in an [CODE(CSS)[[VAR[a]]n+[VAR[b]]]] expression.
-- [Q@en[pseudo-class not supported]]: An unknown pseudo-class
selector appears.
-- [Q@en[pseudo-element not supported]]: An unknown pseudo-element
appears.
-- [Q@en[an+b not closed]]: A pseudo-class which takes an
[CODE(CSS)@en[[VAR@en[a]]n+[VAR@en[b]]]] expression as the argument
is not closed.
-- [Q@en[no attr namespace separator]]: No 
[CODE(charname)@en[[[VERTICAL BAR]]]] character is found
after a [CODE(charname)@en[[[ASTERISK]]]] in an attribute selector.
-- [Q@en[attribute selector not closed]]: An attribute selector is 
not closed.
-- [Q@en[no pseudo-class name]]: Neither pseudo-class name nor
another [CODE(charname)@en[[[COLON]]]] character is found after a
[CODE(charname)@en[[[COLON]]]] character.
-- [Q@en[no pseudo-element name]]: No pseudo-element name is found
after two [CODE(charname)@en[[[COLON]]]] characters.
-- [Q@en[no lang tag]]: No language tag is found in a 
[CODE(CSS)@en[:[[lang]]()]] pseuo-class selector.
-- [Q@en[no local name selector]]: Neither element type name nor 
[CODE(CSS)[[[*]]]] is found after a [CODE(CSS)[[[|]]]] character
delimiting namespace prefix and local name.
-- [Q@en[not not closed]]: An negation selector is not closed.
-- [Q@en[ss after pseudo element]]: A simple selector is found
after a pseudo element appears.
-- [Q@en[an+b syntax error]]: A syntactically invalid
[CODE(CSS)@en[[VAR@en[a]]n+[VAR@en[b]]]] expression is found.
-- [Q@en[no attr local name]]: No attribute local name is found
after a [CODE(charname)@en[[[VERTICAL BAR]]]] character in an
attribute selector.
-- [Q@en[no attr name]]: No attribute name is found in an 
attribute selector.
-- [Q@en[no attr value]]: No attribute value is found after
a matching operator in an attribute selector.
-- [Q@en[no class name]]: No class name appears after a 
[CODE(charname)@en[[[FULL STOP]]]] character.
-- [Q@en[no combinator]]: No combinator appears between sequences
of simple selectors.
-- [Q@en[no contains string]]: No string is specified in a
[CODE(CSS)@en[:[[contains]]()]] pseudo-class selector.
-- [Q@en[lang selector not closed]]: A [CODE(CSS)@en[:[[lang]]()]]
pseudo-class selector is not closed.
-- [Q@en[no attr match]]: Neither attribute matching operator nor
closing character is found in an attribute selector.
-- [Q@en[no sss]]: No sequence of simple selector is found
where it is expected.
- HTML parser
-- [Q@en[after body:[VAR@en[e]]]]
-- [Q@en[after body:/[VAR@en[e]]]]
-- [Q@en[after body:#character]]
-- [Q@en[after frameset:[VAR@en[e]]]]
-- [Q@en[after frameset:/[VAR@en[e]]]]
-- [Q@en[after frameset:#character]]
-- [Q@en[after head:[VAR@en[e]]]]
-- [Q@en[after html:[VAR@en[e]]]]
-- [Q@en[after html:/[VAR@en[e]]]]
-- [Q@en[after html:#character]]
-- [Q@en[bad attribute name]]: There is an attribute whose first 
character is [CODE(char)[[[=]]]], [CODE(char)[[["]]]], or
[CODE(char)[[[']]]].
-- [Q@en[bad attribute value]]: An unquoted attribute value
contains [CODE(char)[[[=]]]], [CODE(char)[[["]]]], or
[CODE(char)[[[']]]].
-- [Q@en[bare ero]]
-- [Q@en[bare etago]]
-- [Q@en[bare hcro]]
-- [Q@en[bare nero]]
-- [Q@en[bare stago]]
-- [Q@en[bogus comment]]
-- [Q@en[bogus end tag]]
-- [Q@en[C1 character reference:U+[VAR@en[HHHH]]]]
-- [Q@en[CR character reference]]
-- [Q@en[charset label detected:[VAR@en[l]]:[VAR@en[m]]]]:
While an HTML document is parsed as in charset [VAR@en[l]],
a [CODE(HTMLe)@en[[[meta]]]] [CODE(HTMLa)@en[[[charset]]]]
declaration with charset [VAR@en[m]] (≠ [VAR@en[l]])
is encountered.
-- [Q@en[dash in comment]]
-- [Q@en[DOCTYPE in the middle]]
-- [Q@en[duplicate attribute]]
-- [Q@en[empty end tag]]
-- [Q@en[empty start tag]]
-- [Q@en[end tag attribute]]
-- [Q@en[image]]
-- [Q@en[in a:a]]
-- [Q@en[in body:[VAR@en[e]]]]
-- [Q@en[in body:#eof]]
-- [Q@en[in button:button]]
-- [Q@en[in CDATA:#[VAR@en[t]]]]
-- [Q@en[in form:form]]
-- [Q@en[in frameset:[VAR@en[e]]]]
-- [Q@en[in frameset:/[VAR@en[e]]]]
-- [Q@en[in frameset:#character]]
-- [Q@en[in head:head]]
-- [Q@en[in nobr:nobr]]
-- [Q@en[in noscript:[VAR@en[e]]]]
-- [Q@en[in noscript:/[VAR@en[e]]]]
-- [Q@en[in noscript:#eof]]
-- [Q@en[in noscript:#[VAR@en[t]]]]
-- [Q@en[in RCDATA:#[VAR@en[t]]]]
-- [Q@en[in select:[VAR@en[e]]]]
-- [Q@en[in select:/[VAR@en[e]]]]
-- [Q@en[in table:[VAR@en[e]]]]
-- [Q@en[in table:/[VAR@en[e]]]]
-- [Q@en[in table:#character]]
-- [Q@en[invalid character reference:U+[VAR@en[HHHH]]]]
-- [Q@en[invalid character reference:U-[VAR@en[HHHHHHHH]]]]
-- [Q@en[isindex]]
-- [Q@en[missing start tag:[VAR@en[e]]]]
-- [Q@en[nestc]]
-- [Q@en[no DOCTYPE]]
-- [Q@en[no DOCTYPE name]]
-- [Q@en[no PUBLIC literal]]
-- [Q@en[no refc]]
-- [Q@en[no space before DOCTYPE name]]
-- [Q@en[no space between attributes]]
-- [Q@en[no SYSTEM literal]]
-- [Q@en[not closed]]: One or more element is not closed by end tags.
The local name of the outermost unclsoed element is given by the
[CODE@en[value]] parameter.
-- [Q@en[not closed:[VAR@en[e]]]]
-- [Q@en[not first start tag]]: The [CODE(HTMLe)@en[[[html]]]]
start tag token is not the first start tag in the input stream.
-- [Q@en[not HTML5]]: A non-conforming [CODE(HTML)@en[[[DOCTYPE]]]]
token where a conformance checker may switch to
another checker for that language.
-- [Q@en[NULL]]: There is a [CODE(charname)@en[[[NULL]]]]
character in the input stream.
-- [Q@en[pio]]
-- [Q@en[string after DOCTYPE]]
-- [Q@en[string after PUBLIC]]
-- [Q@en[string after PUBLIC literal]]
-- [Q@en[string after SYSTEM]]
-- [Q@en[string after SYSTEM literal]]
-- [Q@en[unclosed attribute value]]
-- [Q@en[unclosed comment]]
-- [Q@en[unclosed DOCTYPE]]
-- [Q@en[unclosed PUBLIC literal]]
-- [Q@en[unclosed SYSTEM literal]]
-- [Q@en[unclosed tag]]
-- [Q@en[unmatched end tag:[VAR@en[e]]]]
- [CODE(perl)@en[[[Whatpm::HTMLTable]]]]
-- [Q@en[cell overlapping:[VAR@en[x]]:[VAR@en[y]]]]
-- [Q@en[colspan creates column with no anchored cell]]
-- [Q@en[column with no anchored cell]]
-- [Q@en[rowspan creates row with no anchored cell]]
-- [Q@en[row with no anchored cell]]
- IMTChecker
-- [Q@en[attribute:syntax error:[VAR@en[t]]]]: The parameter name 
[VAR@en[t]] is syntactically invalid.
-- [Q@en[obsolete parameter]]
-- [Q@en[obsolete subtype]]
-- [Q@en[parameter missing:[VAR@en[attribute]]]]
-- [Q@en[parameter not allowed:[VAR@en[attribute]]]]: The parameter
with name [VAR@en[attribute]] is not defined for the media type.
-- [Q@en[private subtype]]
-- [Q@en[private type]]
-- [Q@en[subtype:syntax error:[VAR@en[t]]]]: The subtype name 
[VAR@en[t]] is syntactically invalid.
-- [Q@en[type:syntax error:[VAR@en[t]]]]: The top-level type name
[VAR@en[t]] is syntactically invalid.
-- [Q@en[unregistered subtype]]
-- [Q@en[unregistered type]]
-- [Q@en[value syntax error:[VAR@en[attribute]]]]
- URIChecker
-- [Q@en[default port]]
-- [Q@en[dot-segment]]
-- [Q@en[empty host]]
-- [Q@en[empty path]]
-- [Q@en[empty port]]
-- [Q@en[long host]]
-- [Q@en[lowercase hexadecimal digit]]
-- [Q@en[non-DNS host]]
-- [Q@en[non UTF-8 host]]
-- [Q@en[password]]
-- [Q@en[percent-encoded unreserved]]
-- [Q@en[syntax error:iri3987]]
-- [Q@en[syntax error:iriref3987]]
-- [Q@en[uppercase host]]
-- [Q@en[uppercase scheme name]]
- [CODE(perl)@en[level => unsupported]]
-- [Q@en[address format:[VAR@en[version]]]]: URI address
-- [Q@en[attribute]]
-- [Q@en[addr-spec not supported]]
-- [Q@en[atom|content not supported]]
([CODE@en[value]] is the IMT of the content.)
-- [Q@en[element]]
-- [Q@en[link type:[VAR@en[t]]]]
-- [Q@en[parameter:[VAR@en[attribute]]]]: IMT parameter
-- [Q@en[script:[VAR@en[mt]]]]: Conformance checking
of specified scripting language is not supported.
-- [Q@en[style:[VAR@en[mt]]]]: Conformance checking
of specified scripting language is not supported.
-- [Q@en[subtype]]: IMT subtype
-- [Q@en[type]]: IMT type
-- [Q@en[event handler]]: Validation of event handler attributes is not supported yet.
-- [Q@en[language tag]]: Validation of langauge tags is not supported yet.
-- [Q@en[media query]]: Validation of media queries is not supported yet.