Old tech revamped? One could already do this by including the a tag id at the end of the linked URL. i.e. http://example.com/page.htm#thirdparagraph
One could just insert <null id=thirdparagraph></null> where ever the third paragraph starts.
Although, both of those are possible with the little-known (and little-implemented) XML Linking Language (XLink), a W3C standard. XLink allows one to define links on arbitrary tags, many-to-many links, links between external resources, and links to specific positions and ranges using XPath.
Not sure if that could be a good option to specify some content within a web document. First of all it is not a URL that you can normally use in web browser's address bar and share from social media. Secondly, not sure if it can specify arbitrary part of attribute value.
Thank you for sharing the information anyway and will take a look.