[1] Error levels:

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

[2] Error types:

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