The Web Manifest describes the progressive web applications with meta data and JSON formatting. Browsers parse the manifest file to create the add to homescreen icon and launch the experiences.
Now, instead of polluting each page's HEAD with extra meta data, the browser can load an external file containing standard properties and values formatted using JSON.
The web manifest specification (https://w3c.github.io/manifest/) provides some guidelines for browsers to establish an add to homescreen experience. How browsers implement the experience is left open ended, making an avenue for creativeness. I will cover this topic in more detail after reviewing the manifest file.