About WCAG 2.0 Accessibility

CSE HTML Validator helps an organization comply (but cannot guarantee compliance) with the W3C's Web Content Accessibility Guidelines 2.0 (WCAG 2.0). These are guidelines for web developers and developers of authoring tools to help make them more accessible to people with disabilities. WCAG 2.0 became a W3C Recommendation in December 2008 and builds on and succeeds WCAG 1.0. The W3C recommends that new content use WCAG 2.0.

Developers must satisfy the minimum level of conformance (level A) to conform with WCAG 2.0. See the conformance section of the recommendation for more information. Also, please remember that automated tools like this one, although very useful, can only check certain guidelines and cannot guarantee conformance at any level. Other checking methods are required.

Bracket Info Sections

Most WCAG 2.0 messages will include conformance information in square brackets (we'll call them "bracket info sections"). Below is more information:

There may be one or more of these bracket info sections per WCAG 2.0 message, one for each guideline.

A bracket info section starts with a left square bracket ('['), then the conformance level will be listed first (A, AA, or AAA), then a comma, then a single guideline, then optionally followed by a semicolon and then a comma-separated list of techniques relevant to the guideline, then ends with the right square bracket (']').

When there are multiple bracket info sections for one message, the sections for the lower level of conformance (like "A") will appear before the sections for the higher level of conformance (like "AAA").

Some examples: [AA, 1.4.4; C12, C13, C14] [AAA, 1.4.8; C12, C13, C14] [A, 1.3.2; C27] [A, 2.4.3; C27].

WCAG 2.0 Items Checked (may not be a complete list)

Displays an error message for missing alt text ("alt" attribute) for the "applet", "area", "img", and "input" (when type="image") elements. [A, 1.1.1]

Displays a warning message for alt text that is considered to be too long and not succinct (consider using the "longdesc" attribute). [A, 1.1.1] (New v11.0111)

Displays a warning message if the alt text contains only whitespace. [A, 1.1.1]

Displays a warning message if the alt text is empty but the title text is not. [A, 1.1.1]

Displays a warning message for a missing text alternative (in the body) for "applet" elements. [A, 1.1.1] (New v9.9930)

Displays an error message for missing alternative representation for "object" elements. [A, 1.1.1]

Displays an error message for "input" (of certain types), "select", and "textarea" control elements if they do not have explicitly associated labels and do not have "title" attributes. [A, 1.1.1]

Displays a warning message for empty alternative text (alt="") for the "area" element. [A, 1.1.1] (New v9.9930)

Displays a warning message for missing title text ("title" attribute) for the "area" element. [A, 1.1.1] (New v9.9930)

Displays a message for missing "longdesc" attributes (to specify a text alternative of the frame) in "frame" and "iframe" start-tags. [A, 1.1.1]

Displays a message for missing "longdesc" attributes (to specify a text alternative of the image) in "img" start-tags. [A, 1.1.1] (New v11.0111)

Displays a message about providing a text alternative when the "script" element is used. [A, 1.1.1]

Displays an error message for "a" elements with no link text if "a" doesn't contain any images with alt text [A, 1.1.1]

Displays an accessibility message for image maps. [A, 1.1.1, 2.4.4, 2.4.9]

Displays a warning message if an image appears to be a spacer image and recommends CSS instead. [A, 1.1.1]

Displays a message for form controls that use a "title" attribute (use "title" only when a label cannot be accommodated) [A, 1.1.1, 1.3.1, 3.3.2, 4.1.2]

Displays a message if the alt text is empty or null and there is no title attribute (ensure that such images are decorative or should otherwise be ignored by assistive technology). [A, 1.1.1, 1.2.1] (New v11.0111)

Displays a message about layout tables and the "summary" attribute the first time a "table" element is used. [A, 1.3.1]

Displays a warning message about using header cells if "th" elements are not used in tables. [A, 1.3.1]

Displays a message if the "caption" element is not used in tables. [A, 1.3.1] (New v11.0111)

Displays a message if the "summary" attribute in "table" tags and generates a message if not found. [A, 1.3.1]

Displays a warning message if the "summary" attribute in "table" tags appears to be too terse (it should be descriptive) [A, 1.3.1] (New v11.0112)

Displays a warning message if heading elements appear out of order. [A, 1.3.1]

Displays an error message for heading elements containing no text. [A, 1.3.1] (New v10.0125)

Displays a warning message if a table's caption is the same as the table's summary text. [A, 1.3.1]

Displays a warning message if a layout table is detected and it contains "th" elements, a "caption" element, or a non-empty "summary" element [A, 1.3.1]

Displays a message if a data table is detected with no "summary" or "title" attribute and no caption (ensure the table is properly described) [A, 1.3.1]

Displays a warning message if a "th" element is used without a "scope" or "id" attribute in a data table (clarify the scope of the header cell) [A, 1.3.1] (New v11.0201)

Displays a message (up to 3 times) if a "th" element is used without a "scope" attribute (but with an "id" attribute) in a data table (clarify the scope of the header cell) [A, 1.3.1] (New v11.0201)

Displays a message if more than one "option" element is used but no "optgroup" elements are used. [A, 1.3.1]

Displays a warning message if a presentational attribute is used (like "align"). [A, 1.3.1] (New v11.0114)

Displays a warning message if more than one label is assigned to the same control. [A, 1.3.1] (New v11.9915)

Displays an error message if the "legend" element is not used in a "fieldset" element. [A, 1.3.1, 3.3.2]

Displays an error message if groups of radio or checkbox input elements have the same name value but are not in a "fieldset" element. [A, 1.3.1, 3.3.2]

Displays a message if there are 2 or more form controls in a form that are not in a "fieldset" element (group related form controls with "fieldset") [A, 1.3.1, 3.3.2] (New v11.0114)

Displays an error messages for duplication of unique values (like duplicate "id" values). [A, 1.3.1, 4.1.1] (New v10.0125)

Displays an error messages for "label" references (using the "for" attribute) to nonexistent IDs or to non-labelable elements. [A, 1.3.1, 4.1.1] (New v10.0143)

Displays a message if the "float" CSS property is used (ensure that the visual order matches the source code order). [A, 1.3.2, 2.4.3] (New v11.0111)

Displays a message if absolute positioning (CSS) is used (ensure that the visual order matches the source code order). [A, 1.3.2] (New v11.0111)

Displays a warning message if CSS is used to remove the underline from "a" element link text. [A, 1.4.1] (New v11.0111)

Displays an error message if a color attribute (like "bgcolor", "link", "text", etc.) is used in the "body" tag but not all the color attributes are used [AA, 1.4.3] (New v10.0145)

Displays a warning message if a foreground color is specified without a background color or vice versa in a CSS style rule [AA, 1.4.3] (New v10.0146)

Displays a warning message if a specified foreground and background color is specified in a CSS declaration and the colors do not meet the minimum contrast ratios [AA, 1.4.3; AAA, 1.4.6]

Displays a warning message when the "bgcolor" attribute is used with "text", "link", and/or the "vlink" attribute in the "body" tag and the colors do not meet the minimum contrast ratios [AA, 1.4.3; AAA, 1.4.6]

Displays an error if a font size is specified using an absolute unit (instead of a relative unit like "em" or a percentage) (http://www.w3.org/TR/WCAG20-TECHS/C12, http://www.w3.org/TR/WCAG20-TECHS/C13, or http://www.w3.org/TR/WCAG20-TECHS/C14) [AA, 1.4.4, 1.4.8]

Displays a warning if a font size is specified using an absolute unit and it appears to be for a form control (instead of a relative unit like "em" or a percentage) (http://www.w3.org/TR/WCAG20-TECHS/F80) [AA, 1.4.4] (New v10.0143)

Displays a message if the "height" or "width" CSS property is used with an absolute length for elements that might contain text (like elements other than "img") [AA, 1.4.4] (New v11.0114)

Displays a warning message if the device-dependent "onmouseout" or "onmouseover" event handler attribute is used without a corresponding "onblur" or "onfocus" event handler [A, 2.1.1] (New in v11.0111)

Displays a warning message if the device-independent "onblur" or "onfocus" event handler attribute is used without a redundant "onmouseout" or "onmouseover" event handler [SCR2] (New in v11.9911)

Displays a warning message if the "onfocus" event attribute is "blur()" [A, 2.1.1, 3.2.1; AA, 2.4.7; AAA, 2.1.3] (New v11.0111)

Displays a message about pausing and blinking if it appears that a gif image or animation is specified in the "src" attribute of elements like "img" and "input". [A, 2.2.2] (New v10.0146)

Displays a message for CSS animations and transitions to make sure they don't result in content that may cause seizures in some users. [A, 2.3] (New v12.0037)

Displays an error message for a missing "title" attribute in a "frame" or "iframe" element (requires flag 70 to be enabled). [2.4.1, 4.1.2]

Displays an error message if a page has a missing or empty title (checks the "title" tag, not the "title" attribute). [A, 2.4.2]

Displays a message for "title" elements (ensure that the title is descriptive). [A, 2.4.2] (New v11.0111)

Displays a warning message if the tabindex sequence does not agree with the content sequence. [A, 2.4.3] (New v11.0111)

Displays a warning message when an "a" element containing an "img" element preceeds another "a" element with the same "href" value and where the image alt text is the same as the link text for the adjacent "a" element. [A, 2.4.4]

Displays an error message when the same link text (when "title" attributes are missing, empty, or not unique) links to two or more different resources. [A, 2.4.4] (New v11.0114)

Displays an error message when an "a" element's "title" text appears to be a URL. [A, 2.4.4] (New v12.0011)

Displays a message if any headings are used (ensure that they are descriptive). [AA, 2.4.6] (New v11.0111)

Displays a message if any labels are used (ensure that they are descriptive). [AA, 2.4.6] [A, 3.3.2] (New v11.0111)

Displays a message when the "focus" CSS pseudo-class is used (ensure that the focus indicator is visible). [AA, 2.4.7] (New v11.0111)

Displays a warning message when the the outline is removed from "a" (ensure that the focus indicator is visible). [AA, 2.4.7] (New v14.0106)

Displays an error message if the "lang" and "xml:lang" attributes are not used in the "html" tag. [A, 3.1.1]

Displays a message if the "lang" and/or "xml:lang" attribute is used in the "html" tag (ensure that the specified primary language matches the primary content language). [A, 3.1.1] (New v11.0111)

Displays a warning message if a "dl" element is used without the "title" attribute. [AAA, 3.1.3]

Displays an error message if an "abbr" element is missing a "title" attribute or if the "title" text is empty. [AAA, 3.1.4] (New v12.0011)

Displays a warning message if a form does not appear to contain a submit control. [A, 3.2.2]

Displays an error message when there is an inconsistency with "abbr" elements (like different "title" text for the same abbreviation or different abbreviations for the same "title" text). [AA, 3.2.4] (New v12.0011)

Displays a warning message about changes of context if a "meta" non-zero second refresh tag is found (if AAA conformance checking is enabled) [AAA, 3.2.5]

Displays a warning message if the text "new window" is not found in the link text or in the "title" value of a link with the "target" attribute [AAA, 3.2.5]

Displays a message when the first "form" element is used (ensure that appropriate text messages are used for form errors) [A, 3.3.1, 3.3.2, 3.3.3] (New v11.0114)

Displays a message when the first "form" element is used (ensure that appropriate text messages are used for user input that is not in the list of allowed values or that falls outside the required format or values) [A, 3.3.1, 3.3.3] (New v11.0114)

Displays a message when the first "form" element is used (provide suggestions for correct text/input for user input that is not accepted (when reasonable and possible)) [AA, 3.3.3] (New v11.0114)

Displays a message when the first "form" element is used (provide a way to review/correct data before submission, provide a 'review' checkbox, provide a way to cancel or recover from errors after submission) [AA, 3.3.4] (New v11.0114)

Displays a message when the first "form" element is used (provide a way for the user to recover information that was deleted in error, seek confirmation from the user that the selected action is the intended action, consider providing a 'review' checkbox) [AA, 3.3.4] (New v11.0114)

Displays a warning message for "input" (of certain types), "select", and "textarea" control elements if they have explicitly associated labels but no "title" attribute for context-sensitive help and level AAA checking is enabled. [AAA, 3.3.5]

Displays an error messages for various parsing problems, like problems with start and end tags, HTML comment format, and attribute parsing. [A, 4.1.1] (New v10.0125)

Displays an error message if any CSS errors are found. [A, 4.1.1] (New v11.0111)

Displays a message for HTML5 documents or warning message for HTML 5.1+ documents about using only the well-supported elements and parts of HTML5/HTML 5.1 or using the latest mature version of HTML. [A, 4.1.1] (Updated v14.00)

Displays an error messages for blank (empty) label text. [A, 4.1.2] (New v10.0143)