scala binary vs scala full version convention - scala

Question

I am readying the following sbt page:
https://www.scala-sbt.org/1.x/docs/Cross-Build.html#Cross-building
But i find the documentation not that great, and would like to clarify something which i think i understand but is not made explicit in the doc.
What is the convention for :
CrossVersion.binary (_<scala-binary-version>)
CrossVersion.full (_<scala-version>)
In other words i want a simple example of
_<scala-binary-version>
and of
_
is it :
Binary Version example 2.12
Scala version example 2.12.12
Is that the difference between a binary version and the scala version, where the later would include the compiler access and what not ?
EDIT1
The following example is given in the page:
These are equivalent:
"a" %% "b" % "1.0"
("a" % "b" % "1.0").cross(CrossVersion.binary)
This overrides the defaults to always use the full Scala version instead of the binary Scala version:
("a" % "b" % "1.0").cross(CrossVersion.full)
I only understand what is meant is the second statement, because i have been using the first and know what it does. But it is a guess, and i am just looking for an explicit confirmation with an example, which i believe could benefit any new scala dev in their journey.

Answer 1

So 2.12.12 is a full version (as well as a patch version) and 2.12 is a binary version.
Binary versions are useful because libraries compiled using a different but binary compatible version can be used in your project without any problems. For example, if you are using Scala 2.13.3 you can use a library that was compiled using 2.13.0 or 2.13.4 but not one compiled using 2.12.12.
The full version is useful for things that access the underlying compiler API which doesn't retain binary compatibility, for example, compiler plugins like the kind projector.
BTW, just for fun, 2.13.0-RC1 is another full version but not a patch version.