It’s an implementation of ODK[1] extensions to the XForms specification[2]. The specific implementation is Enketo[3], which I was brought on to ODK to help maintain. Not exactly the spec I’d go with greenfield, but it’s been successfully in use for a decade with great impact.

1: https://getodk.org/

2: https://getodk.github.io/xforms-spec/

3: https://enketo.org/

ideas:

could be using data returned in XML format because there is no JSON endpoint for that particular data source.

XPath is also nice for dealing with just about any complex markup tree, for example if you needed to extract data from serialized DOMs that were sent to your application somehow.

How about SVG tools using XPath?

Thanks, great ideas and I'd never considered XPath for SVG. I need to delve into that one further.