What does it mean in the instruction ?

[Manish Kumar]

Design decisions should be briefly but clearly described in your comments.

What does the word 'comments' mean here in the instruction file? Does it mean the Javadoc comment or the Design choice file?
Now i'm working on documentation and have got confussed over that ..
Please help me.
with regards
Manish

[Rama Ituarte]

The design doc