1. Why do I use vspace{0pt}? The default reference point for minipage alignment is the baseline, i.e., b= ottom. To release it, one needs to use \vspace{0pt}, a trick I learned from= questions about minipage alignement in the Internet a while back, then jus= t know such usage. In the beginning, I did not kwnow the reason behind it e= ither, but persistent research pays off, one day, I saw a blogger mentioned= this point in this website. When your question arised, I tried it out and = it works. So puzzle confirmed and solved.=20 2. Yes, in theory, a new environment needs not another environment in it. B= ut, often time, a new environment is used to modify an existing environment= , to expand the existing one. In this particular case, the questioner wants= to establish a connection with the higher level section counter. This is w= hat the questioner wants because he/she defined it, not me. This also demon= strates an MWE is important when one asks a LaTeX question.