This case makes me wonder what if traditional filesystems would not separate files and directories. So that there would be just files which may have data and sub files. Then html file could include all js files etc. directly inside it so that we could give multi file permissions without leaking it to siblings.
The feature you are looking for already partially exists. Look for "extended attributes" (for most filesystems) or "alternate data streams" (for NTFS).
But in this case, it's much simpler to make a tar or a zip with the HTML and all necessary files. eg. that's how Python "eggs" work.
