Description of Errors

HTML5 Parse Errors in Tokenization Stage

There are two attributes with same name.

Attributes must be unique in an element. Specifying attributes with same name more than once is non-conforming.

The motion attribute is not part of the HTML standard. Use img element with animation GIF instead.

Void element syntax (`/>`) cannot be used for this element.

The void element syntax /> syntax can only be used for base, link, meta, hr, br, img, embed, param, area, col, and input elements. For any other elements, using that syntax is non-conforming.

Unlike XML, the void element syntax (/>) has no effect in HTML.

Element Content Model Errors

Data character is not allowed in this context.

A data character occurs where it is not allowed in this context. The document is non-conforming.

Possible causes:

If the erred element is an inline-level element (such as a or span)

A data character cannot be a child of certain sectioning elements such as body, section, and blockquote.

Any inline-level content must be put in e.g. paragraph element such as p.

If the erred element is a block-level element (such as div or hn)

Though some elements such as div, li, and td allow either one of block-level or inline-level content is allowed. If there is a block-level content, any inline-level content must be put in e.g. paragraph element such as p.

There must be a `$0` element as a child of this element.

The content model of the element is so defined that it must contain a $0 child element. Without such an element, the document is non-conforming.

For example:

The head element must contain exactly one title child element.
The tr element must contain one or more td or th child element.

There must be a `td` or `th` element as a child of this element.

The tr element must contain at least one td or th child element. Without such an element, the document is non-conforming.

This element is not allowed in this context.

An element occurs where it is not allowed. The document is non-conforming.

Possible causes:

If the erred element is an inline-level element (such as a or span)

An inline-level element cannot be a child of certain sectioning elements such as body, section, and blockquote.

Any inline-level content must be put in e.g. paragraph element such as p.

If the erred element is a block-level element (such as div or hn)

If the erred element is the root html element

In an XHTML document, the root html element must have an xmlns attribute whose value is set to http://www.w3.org/1999/xhtml.

Unsupported Messages

This attribute is not supported by the conformance checker; it might or might not be conforming.

The conformant checker does not support the attribute. It cannot determine whether the document is conforming or not.

This element is not supported by the conformance checker; it might or might not be conforming.

The conformant checker does not support the element. It cannot determine whether the document is conforming or not.

The link type `$0` is not standardized or registered at the time of the release of the conformance checker; it is non-conforming unless it has now been registered.

The rel attribute is defined as a list of link types. Some common link types are defined in the HTML5 specification. Additional link types can be registered to the WHATWG Wiki. use of any other link type is non-conforming.

The specified link type is not part of the standard or registry when the database used by the conformance cheker is created. The link type might have been added to the registry since then. In such case it might be conforming. Otherwise, the document is non-conforming.

HTML5 Parse Errors in Tokenization Stage

There are two attributes with same name.

Void element syntax (`/>`) cannot be used for this element.

HTML5 Parse Errors in Tree Construction Stage

The `$0` element cannot be inserted between `head` and `body` elements.

This document does not start with the `DOCTYPE` declaration.

Element `$0` is not closed.

This document is written in an old version of HTML.

Element `$0` is not opened.

Element Content Model Errors

Data character is not allowed in this context.

There must be a `$0` element as a child of this element.

There must be a `td` or `th` element as a child of this element.

This element is not allowed in this context.

Attribute Value Errors

This attribute only allow a limited set of values and the specified value is not one of them.

Table Model Errors

The table has no cell (`td` or `th`) in the last row.

Internet Media Type Warnings

An obsolete subtype is used.

A private (`x-` or `x.`) subtype is used.

The subtype is not registered to IANA.

URI (or IRI) Errors

This string is not an IRI syntactically.

URI (or IRI) Errors

This IRI should explicitly end with `/`.

Unsupported Messages

This attribute is not supported by the conformance checker; it might or might not be conforming.

This element is not supported by the conformance checker; it might or might not be conforming.

The link type `$0` is not standardized or registered at the time of the release of the conformance checker; it is non-conforming unless it has now been registered.

License of This Document

Description of Errors

HTML5 Parse Errors in Tokenization Stage

There are two attributes with same name.

Void element syntax (/>) cannot be used for this element.

HTML5 Parse Errors in Tree Construction Stage

The $0 element cannot be inserted between head and body elements.

This document does not start with the DOCTYPE declaration.

Element $0 is not closed.

This document is written in an old version of HTML.

Element $0 is not opened.

Element Content Model Errors

Data character is not allowed in this context.

There must be a $0 element as a child of this element.

There must be a td or th element as a child of this element.

This element is not allowed in this context.

Attribute Value Errors

This attribute only allow a limited set of values and the specified value is not one of them.

Table Model Errors

The table has no cell (td or th) in the last row.

Internet Media Type Warnings

An obsolete subtype is used.

A private (x- or x.) subtype is used.

The subtype is not registered to IANA.

URI (or IRI) Errors

This string is not an IRI syntactically.

URI (or IRI) Errors

This IRI should explicitly end with /.

Unsupported Messages

This attribute is not supported by the conformance checker; it might or might not be conforming.

This element is not supported by the conformance checker; it might or might not be conforming.

The link type $0 is not standardized or registered at the time of the release of the conformance checker; it is non-conforming unless it has now been registered.

License of This Document

Void element syntax (`/>`) cannot be used for this element.

The `$0` element cannot be inserted between `head` and `body` elements.

This document does not start with the `DOCTYPE` declaration.

Element `$0` is not closed.

Element `$0` is not opened.

There must be a `$0` element as a child of this element.

There must be a `td` or `th` element as a child of this element.

The table has no cell (`td` or `th`) in the last row.

A private (`x-` or `x.`) subtype is used.

This IRI should explicitly end with `/`.

The link type `$0` is not standardized or registered at the time of the release of the conformance checker; it is non-conforming unless it has now been registered.