## 1 Introduction
### State of the Art on XR and Accessibility for Cultural Heritage
Tracking technologies would have required software updates to ensure content enjoyment over time, whereas the navigation of reconstructions through 360\({}^{\circ}\) panoramas on a 'liquid' (to be enjoyed on various devices) web-based platform ensures a wider spread of use. Tracking devices to be used in situ would have required the presence of museum staff trained in the operation and maintenance of the installations, which museums cannot always provide. The latter is often the cause of the decline and non-use of many technological applications. Another important aspect related to archaeological and museum enhancement concerns accessibility in its various forms: spatial, sociocultural, cognitive and psycho-sensory inclusion. According to ISO 9241-11:2018 [23], the term \"accessibility\" refers to the extent to which products, systems, services, environments and facilities can be used by people in a population with the widest range of user needs, characteristics and capabilities to achieve an identified goal in an identified context of use. As a public place of education and culture, the museum encourages collective communication, sharing and social exchange. The new 'Museum' definition drawn up by ICOM in 2022 [24] emphasises that \"open to the public, accessible and inclusive, museums foster diversity and sustainability\". The concept of accessibility in its declinations promotes a whole series of actions based on the universal design principles, as theorized in 1997 [25], built to respond to the specific needs of people, through the diversification of multisensory contents able to stimulate the participation of all [26]. Despite the principles of UD, the focus of institutions, designers and architects was initially mostly on users with physical difficulties and in wheelchairs; thus, the legislation was mainly addressed to measures and prescriptions of space sizes rather than to \"solutions for all\". Gradually, a growing awareness of better inclusion of larger users' needs took place, also extending to different sensorial and cognitive difficulties. In December 2019, a new version of the European guideline \"accessibility requirements for Information and Communication Technologies (ICT) products and services\" [27] was published to specify functional accessibility requirements applicable to ICT products and services, to be used in public procurement in Europe. This standard has been drawn up under the competence of the authority federated to \"Ente Italiano di Normazione\" (UNI), \"Tecnologie informatiche e loro applicazioni\" (UNINFO) and became part of the Italian national legislation on 17 December 2020. The document is suitable for web-based technologies, non-web technologies and hybrid technologies using both. It includes software, hardware and services. Most parts of the principles here established are addressed to improve the accessibility and usability of multimedia applications and comfort of use by people who are blind and deaf or by visitors with limited abilities in vision and hearing, visitors in wheelchairs and persons with cognitive disabilities. However, they can improve the experience of all users, generating ease of use and well-being. This means that information has to be delivered not only by means of a unique media/sensory solicitation but more than one. In the specific field of museums and archaeological sites, creating accessible content means allowing their fruition also to those who cannot physically go to the sites, or who cannot perceive using the five senses, diversifying the type of language (text, audio,pictures), integrating tangible interface [28; 29] and distinguishing the communication format in order to reach both a generic and a specialised audience. In the latter case, it is crucial to accompany the virtual reconstructive hypotheses with the scientific data that supported and directed them to share the reliability of the reconstructions, the sources and the interpretative processes adopted.