Introduction to the Special Issue on W4A’21

We are pleased to present the first Special Issue on the International Web for All Conference (W4A) series featured in the ACM Transactions on Accessible Computing (TACCESS) journal. This volume presents seven articles that are extended versions of the conference papers presented at the 18th International Web for All Conference, which was held online on April 19–20, 2021. Authors of several top papers from the conference submitted manuscripts for consideration, which then underwent a full journal review process. The guest editors for this issue are Victoria Yaneva (National Board of Medical Examiners, USA; University of Wolverhampton, UK) and Dragan Ahmetovic (University of Milan, Italy). The guest editors thank the authors for their excellent submissions, and they also thank all of the journal reviewers who contributed their time and expertise to this process. The first article, titled “AccessComics2: Understanding the User Experience of an Accessible Comic Book Reader for Blind People with Textual Sound Effects,” proposes an accessible digital comic-book reader for people with visual impairments. Surveys and interviews with participants who are blind or have low vision revealed preference for the inclusion of brief scene descriptions and sound effects. These components were integrated into the system and further evaluated, showing that the presence of scene descriptions was useful for concentration and understanding, while the sound effects made the book reading experience more immersive and realistic. The second article, “The Transparency of Automatic Web Accessibility Evaluation Tools: Design Criteria, State of the Art, and User Perception,” presents a comprehensive survey of the instruments available for automated website accessibility evaluation, the metrics they adopt, and how these are presented to the user. Through a survey with 138 users of evaluation tools and a study with 18 accessibility and web design experts, the authors identify a number of design criteria aimed to support the transparency of the reported results and their interpretability by end-users. The third article, “The Accessibility of Data Visualizations on the Web for Screen Reader Users: Practices and Experiences during COVID-19,” explores the level of accessibility of web-based data visualizations by screen reader users. To this end, the authors conduct an accessibility audit of 87 data visualizations by 3 expert auditors, a follow-up survey with 127 screen reader users, and an observational study with 12 participants interacting with accessible web visualizations. A final discussion proposes recommendations for designing more accessible data visualizations. The fourth article, “WordMelodies: Supporting the Acquisition of Literacy Skills by Children with Visual Impairment through a Mobile App,” presents a mobile app designed to support inclusive teaching of literacy skills for primary school students. The app includes over 80 different exercise types in Italian and English with adjustable difficulty levels. Evaluation with primary