Financial & competing interests disclosure
The work described in this paper was supported by the General Research Fund from the Research Grants Council of the Hong Kong Special Administrative Region, China (ref. no. CUHK14107415), awarded to PS Leung. The author has no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.
No writing assistance was utilized in the production of this manuscript.