Unique Dirty Partial- "where some includes none or all bytes"

Hi.
I have a question about Unique Dirty Partial.
When I see the spec about Unique Dirty Partial, It is explained as below.
"The cache line is unique. The cache line might have some bytes valid, where some includes none or all bytes."

I can't understand "The cache line might have some bytes valid, where some includes none or all bytes"
Does this mean that there may be a some valid byte in the cache line, and the some valid area is all-valid or non-valid?

Thanks in advance.