Not sure if this is possible, but I think Divi does something like this. Say I design a block or element or section of a website, and I want to easily reuse this again in the future on other websites, instead of just copying and pasting, I would like to be able to save it as a Custom Element, so I just find it in a custom element tab, and click it and there it is on the page.
Related, not sure if this is already possible, but say i set up a block of text, with some bold, some fonts, colors, I would like to be able to save that to reuse later in other websites.