It's bound to happen, but it's something that almost nobody working on a new project wants to deal with -- standardization. Or productization, or some other -ization, of which there are far too many. But it's that point at which you need to look at things and decide that things have gotten large enough that it's time to say "This Will Not Change" and be done with it. It's got to be done, of course, if you ever want a project to move past the toy stage.
Parrot's been doing this in fits and starts as we go along, though up until now many of the "permanent" decisions (for some fairly variable definition of permanent) have been more design things than implementation things. Most of the opcodes have been pretty permanent, but that's about it. Most of the rest is firm but not really fixed, at least not officially. Today, though.... today we start making things official.
In this case, we're officially mapping out the basic variable types that parrot will ship with. (The guarantees here are for a normal version of parrot--stripped down versions may have fewer of these) Nothing fancy--basic undef/int/float/string/bool PMC types and their array variants, plus some of the types parrot uses internally (such as the environment PMC and ordered hash we use for namespaces and pads) but they need defining, so... they're defined. Up until now folks have been generally using the Perl* variants, but besides being distasteful to some, those classes do more than a basic type ought, so this'll be good there.
If you're following along with docs, these types are defined in PDD 17, Basic Types.