I guess a better way to say what I meant is "common design language." Things that become components in some component library.
They aren't written down, set in stone, spec'd in any way, but for example:
* the idea of a hero image with a headline and a sub headline followed by a call to action is common on many SaaS product websites.
* news websites all look very coherent, so they've adopted some sort of typographical rhythm just like they would in a print publication
* the multitude of component libraries means advanced UI can be programmed with some readymade parts, diminishing the need to write custom CSS for something like an image carousel (for a trivial example)
