

This makes it a great solution with many interesting use cases: split an app into bundled components that you can distribute as building blocks, better manage dependencies to avoid redundancy, code organization, etc.

That includes HTML, CSS, JavaScript or anything else an. HTML Imports, part of the Web Components, allows to bundle HTML documents in other HTML documents. Few mentioned in this question and not very reliable. It is not ideal because it depends on scripting techniques, thus making the execution slower and more complex, among other drawbacks.
The HTML