This success criterion is now considered to pass for all HTML and XML-based content. It no longer needs to be evaluated.


Version: WCAG 2.0 and up
Number: 4.1.1
Level: A


The purpose of this success criterion was to ensure that critical markup errors do not cause user agents and assistive technologies to interpret documents differently. It was primarily aimed at HTML content, as XML has a rigid parsing model that often results in pages with errors not rendering for any users (i.e., errors are general usability issues, not specifically accessibility ones).

Since the HTML standard now defines an algorithm for correcting mistagged content, this success criterion no longer applies to its original case.


The change to success criterion 4.1.1 still has to work its way through the W3C publishing process. It is not yet official. As XHTML is far more significant to EPUB, and already captures the parts of the success criterion not covered elsewhere in WCAG, the knowledge base and SMART checker assume the change will be enacted.

How to Meet

All HTML and XML-based content passes this success criterion. No evaluation steps are required.

It is, however, still strongly recommended to validate all digital publications for markup errors and warnings. This step may still capture accessibility issues related to other success criteria. For example, duplicate IDs are an accessibility problem when they break the use of ARIA attributes for custom controls, prevent users from reaching linked descriptions, break skip to content links, etc.

The following table provides an overview of parsing errors that affect the accessibility of digital publications as well as which success criteria they should be reported under:

Issue Report under
More than one role attribute on an element with conflicting values 1.3.1
Duplicate ID causes mis-labelled controls 4.1.2, 1.3.1
Duplicate ID causes reference to incorrect table header 1.3.1
Duplicate ID breaks skip to content link 2.4.1
List items not contained in a list element 1.3.1
Invalid nesting of interactive elements, such as a link inside a link or button 1.3.1, 2.1.1, 4.1.2

Additional Information

The following knowledge base pages provide more information about how to address this success criterion for publishing content: