woothemes/woocommerce — comment on commit 7b375a851c4afc46152194d442afcfa274f2626d
File:  line 0
By GeertDD:

It looks like most classes use dashes, e.g. "order-number". Yet some use underscores: "order_details" and "customer_details".

Is there a specific reason for that? If not, more consistency would be better. I'd prefer dashes, which is used WordPress classes too in most cases.