## 2 Related Work  
Web browsers are becoming more and more integrated with devices' hardware. There is already a vast literature on interactive presentation of 3D content using WebGL--a JavaScript API for rendering high-performance interactive 3D and 2D graphics without the use of plug-ins [2]. However, a web page today can also obtain access to different hardware and sensors, on a variety of devices [3], allowing to create and deliver rich web-based experiences that go beyond the mere 3D presentation, without requiring any additional software for final users. A web-application can access camera and microphone for instance, access user location (geolocation API), device orientation and position (landscape/portrait). A web-app can detect network type and speed, battery status and available memory, as well as preventing mobile device screen to standby (wake lock API). WebRTC [4] introduced an API that gives browsers the ability to communicate in real-time, to stream video, voice and generic data between peers. A few web browsers also already provide support for speech recognition and synthesis, through the Web Speech API (https://developer. mozilla.org/en-US/docs/Web/API/Web_Speech_API, accessed on 22 November 2021). All these integrations can be used to craft web-based, interactive CH applications that can be consumed by final users just by opening an URL on their devices. Recent literature is also investigating privacy concerns [5] of HTML5 web-applications. Indeed, depending on the hardware/sensor accessed, specific features require A) a secure connection (certified domain)--for instance accessing built-in microphone or camera; and B) user consent. **Immersive VR and AR on the Web--**The introduction of the first WebVR open specification [6] allowed developers and designers to create seamless immersive realities in common web browsers using consumer-level 3-DoF and 6-Dof HMDs. Because of its inherent openness and accessibility, the web represents a great opportunity to enable universal access to immersive VR experiences, without requiring additional software. The specification played a big role in democratizing immersive VR by allowing larger audiences to experience 3D content through low-cost (e.g., cardboards) or high-end headsets (HTC Vive, Oculus Rift, Oculus Quest, etc.) directly from a web page. The open specification evolved into WebXR ([[https://immersiveweb.dev/](https://immersiveweb.dev/)]([https://immersiveweb.dev/](https://immersiveweb.dev/)), accessed on 22 November 2021) [7;8]: it aims to unify VR and AR (Augmented Reality) worlds, supporting a wide range of user inputs (e.g., voice, gestures) enabling users to navigate and interact with virtual spaces over the web [9;10]. WebXR allows entirely new, gripping experiences to be built for the web, and it is also fueling content creators who need to test and deploy immersive VR content on the web. WebXR is also being used for creative narratives in CH through immersive AR experiences [11] or toolkits for creating XR digital storytelling [12]. It is also possible for a web page to access VR controllers haptics, and even track articulated hand poses (at the present time, as experimental feature) allowing hand tracking with supported HMDs (e.g., Oculus Quest) in WebXR spaces. **Standardization of Web3D formats--**_glTF_ ([[https://www.khronos.org/gltf/](https://www.khronos.org/gltf/)]([https://www.khronos.org/gltf/](https://www.khronos.org/gltf/)), accessed on 22 November 2021) (GL Transmission Format) by Khronos is a royalty-free, open standard for efficient streaming and rendering of 3D models and scenes [13]. It minimizes the size of 3D assets and the runtime processing required to unpack and use them. glTF is an extensible publishing format that streamlines authoring workflows and interactive services by enabling the interoperable use of 3D content across the industry.