Why Spring makes me sick #15

From the Spring Framework Reference Documentation:
"There are a few restrictions due to the fact that CGLIB dynamically adds features at startup-time:

• Configuration classes should not be final
• They should have a constructor with no arguments"

WTF do they mean by should? "Should" implies that these things are optional.

But in fact they are not - I had to write tests to check it.
A documentation, which is not specific can be quite useless...