I wondered why "emerge bash-completion" merges gentoo-bashcomp _after_ bash-completion and found that the bash-completion ebuild has a PDEPEND variable. I looked into the Gentoo Developer Handbook and /usr/portage/skel.ebuild, but couldn't find anything about it. Reproducible: Always Steps to Reproduce:
both documents you mention are HOWTO-type documents, they are not manuals if you read the notes in the Developer Handbook, it tells you to read `man 5 ebuild` for an exhaustive list of everything you ever wanted to know about ebuilds