How can I learn which techniques can be used for HTML DOM element identification? I have recently seen two similar codeless services, a web data extractor and an automated test builder for web frontends. browse.io and Virtuoso.

They both allow a user to

- label DOM elements displayed in a browser and record data from them.

- are self-healing, so the labelled element is still selected when the XPath of a DOM element changes.

I am curious how they could achieve this. Is there an open-source library or a cloud tool which provides the functionality to identify HTML elements? or does the need custom models?