The ebuild HOWTO and DevManual use all over suboptimal examples with versions like ruby-2.6 etc. while they should rather show more useful cases when the minor number is > 10. For example, how can I require perl-5.6? I have perl-5.16 installed but emerge complains the depenedency is not fullfilled.
The devmanual really aims to give an example. Perhaps not the best and neither the most complicated ones. Your best resource on understanding ebuilds is to just read the ebuild tree yourself. Devmanual can't possibly explain everything. In this particular case, perl, if you find that you need more guidance to write perl ebuilds, talk to the perl team (or open a bug for them) to improve their documentation or submit an item for the devmanual.
