MKV Ordered Chapters SegmentFilename + SegmentUID?

[patrick_]

When specifying in MKV Ordered Chapters SegmentFilename and SegmentUID, what will happen?

- the first entry will be used
- the last entry will be used
- the specified filename will be the first to check if it matches the SegmentUID, if it doesn't match, other files will be checked.
- the filename will be used (without checking the UID), but if the file hasn't been found, it will fallback to SegmentUID
- ....

The point of specifying both is to reduce disk load.

Thanks in advance.