Footnotes

• Contributors All authors wrote components, edited the manuscript and approved the final draft. All authors confirm that they have contributed to this article and met the following three requirements: (A) they made significant contributions to the conception, design and implementation; (B) they drafted or revised the article for intellectual content; and (C) gave final approval of the submitted article.

• Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

• Competing interests None declared.

• Provenance and peer review Not commissioned; internally peer reviewed.