Automated navigation index within a page. Local Nav builds an in-page navigation index with smooth scrolling navigation and back to top options.
Local Nav is like an Autonav block, except it provides navigation within a long page. You specify a few parameters for how Local Nav picks out headings in a page. When the page loads, the Local Nav block will scan the page content and build an in-page navigation index of links within the page.
Smooth scrolling uses a browser scrolling API with a recommendation for smooth scrolling. The scroll rate and whether it is smooth or snap are up to the visitor's browser and any preferences they may have configured.
For details and examples, see https://c5magic.co.uk/addons/local-nav.