I am not sure where you read that but the syntax you propose is invalid. A package declaration must follow the syntax:
PackageDeclaration:
Annotations
opt
package PackageName ;
So you could have an annotation before the package
keyword, but that's it. For example, public package a.b.c;
is not a valid statement and generates the following compilation error with javac (in jdk 8):
Test1.java:5: error: class, interface, or enum expected
public package a.b.c;
1 error
Note: It seems that public package a.b.c;
compiles with some compilers. That looks like a bug since it does not match the language specification.