Understanding translation output

Q1. So where is a help file on interpreting the output of the perl BLEU script? What do these things mean?

The output is:
PRED
PRED SCORE
GOLD
GOLD SCORE

I can only guess what these are:
PRED = model prediction
PRED SCORE = ?? Predicted score WITHOUT seeing truth data ??
GOLD = target truth data (ie human translation)
GOLD SCORE = ?? ACTUAL score of prediction compared to truth data ??

IGNORE Q2, I’ve read about SentencePiece now . .
Q2. What does it mean if the PRED has an _ before each word (and under each first letter)?
eg: PRED 270: ▁Und ▁die s ▁in ▁aller ▁Ruhe .

Here are some information regarding “SCORE”: