Looks like the answer is that +
includes an implicit upper bound. So 1.+
means "any version that starts with 1.
"
This doesn't seem to be anywhere in the Gradle docs, but it is documented for Ivy:
- end the revision with a +
selects the latest sub-revision of the dependency module. For instance, if the dependency module exists in revision 1.0.3, 1.0.7 and 1.1.2, "1.0.+" will select 1.0.7.