Question: How does explicit constraint on the KL divergence term that authors propose looks like?
Answer: Answer with content missing: (Formula 2) Formula 2 is an answer: 
\big \langle\! \log p_\theta({x}|{z}) \big \rangle_{q_\phi({z}|{x})}  -  \beta |D_{KL}\big(q_\phi({z}|{x}) || p({z})\big)-C|