Added a few comments
Added a few comments


Former-commit-id: abf26a12ddf9e33e14f0596b3a52f3da7c5013b1 [formerly da5f99a9d2310fcf60613e9c3356bde28f9bf7b8]
Former-commit-id: 399914ac2cc7fbdc95ce8ef791a7d3471560579b
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine