Errors and Warnings – Web Accessibility Check Using Aspose.HTML

Aspose.HTML for .NET provides the Aspose.Html.Accessibility namespace, which is intended for all web accessibility related manipulations and checks. This article will examine classes and interfaces that help collect error and warning information when checking a website’s accessibility against WCAG compliance. We will pay particular attention to the failure criteria and methods that report errors and look at a C# example of getting web accessibility errors after validating an HTML document.

You can learn how to use the AccessibilityValidator class to programmatically check web accessibility from the article Accessibility Validator – Website Accessibility Check in C#.

Detecting errors helps identify barriers that may prevent people with disabilities from using and interacting with web content effectively. Errors and warnings guide what must be addressed to improve web accessibility. They serve as a roadmap for developers and designers to make necessary changes.

IError

The IError is a public interface containing information about the validation error. This means an erroneous check, i.e., the rule was not passed – and its result does not match Accessibility.

Property	Description
ErrorMessage	Returns a string message of the error or warning.
Target	Returns an HTML or CSS element where the error was found. The returned object is of type Target.
ErrorTypeName	Description of the presentation of the error object. It has two options “Error” or “Warning”.
ErrorType	Returns error type numeric value.
Success	Result of this object.

IError object has such meanings:

* ErrorType = 1 and Success = false – this means that the error is critical, and the result of the check is not performed.
* ErrorType = 2 and Success = true – this means that the error is not critical but has an informational character and displays hints for possible improvement. 

The type of error is determined by the type of technique:

• If a technique fails to meet a required success criterion, and that criterion is required to meet it, the result will be marked as a critical failure, resulting in ErrorType=1 and Success=false, and it is an Error.
• If a technique is not strictly required, or if the issue is more of a best practice or improvement suggestion than a hard violation of the rules, it will be marked as ErrorType=2 and Success=true, and it is a Warning.

Target

The Target is a public class that contains item of HTML or CSS element of document where the error was found.

Property	Description
Item	Returns Object of html or css element.
TargetType	Returns the type of the contained object. Object type of TargetTypes.

TargetTypes

The TargetTypes Enum of element types from the HTML document containing the error:

Value	Description
HTMLElement	The element containing the HTMLElement from document.
CSSStyleRule	The element containing the CSSStyleRule from document.
CSSStyleSheet	The element containing the CSSStyleSheet from document.

Let’s look at the C# code for iterating through the web accessibility check results, paying particular attention to the failure criteria and the details of the methods that report errors. Example of getting errors details and elements of an HTML document:

1. Use the RuleValidationResult class and iterate through the ruleResult objects contained within validationResult.Details. These represent different accessibility criteria.
2. Print the code and description of the criterion and whether it was successful or not. For this, use the Code and Description properties of the IRule interface.
3. Use the Success property to check the criteria.
4. Use the ITechniqueResult objects – ruleDetail contained within ruleResult.Errors. The ITechniqueResult objects represent individual rule results for the criterion that reported errors.
5. Print the information about the method, including the method code, success status, and description.
6. Use the IError property to obtain the error object from the ruleDetail. The ruleDetail represents a specific accessibility issue, and the error object contains information about that issue.
7. Use the Target property to retrieve the target object associated with the error. The target object typically represents the specific HTML element, CSS rule, or other content that triggered the accessibility error.
8. Print information about the error. It includes the error type (error.ErrorTypeName) and the error message (error.ErrorMessage).
9. Use the TargetType property of the Target class to check the type of the target object. Depending on the type of the target object, specific information is extracted and printed to the console.

// Check HTML for WCAG compliance and output failed rule codes and error messages

// Initialize a webAccessibility container
WebAccessibility webAccessibility = new WebAccessibility();

// Create an accessibillity validator with static instance for all rules from repository that match the builder settings
AccessibilityValidator validator = webAccessibility.CreateValidator(ValidationBuilder.All);

string documentPath = Path.Combine(DataDir, "input.html");

// Initialize an object of the HTMLDocument class
using (HTMLDocument document = new HTMLDocument(documentPath))
{
    // Check the document
    ValidationResult validationResult = validator.Validate(document);

    foreach (RuleValidationResult ruleResult in validationResult.Details)
    {
        //  list only unsuccessful rule
        if (!ruleResult.Success)
        {
            // print the code and description of the rule
            Console.WriteLine("{0}:{1} = {2}", ruleResult.Rule.Code, ruleResult.Rule.Description, ruleResult.Success);
            // print the results of methods with errors
            foreach (ITechniqueResult ruleDetail in ruleResult.Errors)
            {
                // print the code and description of the method
                StringBuilder str = new StringBuilder(string.Format("\n{0}: {1} - {2}",
                                                           ruleDetail.Rule.Code, ruleDetail.Success,
                                                           ruleDetail.Rule.Description));
                // get an error object 
                IError error = ruleDetail.Error;
                // get a target object 
                Target target = error.Target;
                // get error type and message 
                str.AppendFormat("\n\n\t{0} : {1}", error.ErrorTypeName, error.ErrorMessage);
                if (target != null)
                {
                    // Checking the type of the contained object for casting and working with it
                    if (target.TargetType == TargetTypes.CSSStyleRule)
                    {
                        ICSSStyleRule cssRule = (ICSSStyleRule)target.Item;
                        str.AppendFormat("\n\n\t{0}", cssRule.CSSText);
                    }
                    if (ruleDetail.Error.Target.TargetType == TargetTypes.CSSStyleSheet)
                        str.AppendFormat("\n\n\t{0}", ((ICSSStyleSheet)target.Item).Title);

                    if (ruleDetail.Error.Target.TargetType == TargetTypes.HTMLElement)
                        str.AppendFormat("\n\n\t{0}", ((HTMLElement)target.Item).OuterHTML);
                }
                Console.WriteLine(str.ToString());
            }
        }
    }
}

See Also

• In the chapter Web Accessibility Check, you will learn how to check website accessibility for all WCAG compliance or only meet specific criteria using classes and methods of the Aspose.Html.Accessibility and Aspose.Html.Accessibility.Results namespaces.
• The article How to Improve Website Accessibility explains how to make your website accessible to users and how to check your website for WCAG compliance using the Aspose.HTML API for .NET.
• The article Screen Reader Accessibility explains how to design a website for screen reader accessibility in accordance with WCAG guidelines using the Aspose.HTML for .NET API.
• In the article Accessibility Validator, you will learn about the AccessibilityValidator class that can be used to test web accessibility rules such as principles, guidelines, and criteria.
• In the article Web Accessibility Rules, you will learn how to use the AccessibilityRules class, which is a repository of WCAG 2 requirements, success criteria, and techniques, for web accessibility checks.

Aspose.HTML offers free online Web Accessibility Checker. This tool scans web pages, validates them for WCAG compliance, identifies problems, and suggests improvements. Get instant insights into your website’s compliance, allowing you to determine the scope of necessary corrections and the gap between the current state of your website or HTML document and WCAG requirements.