Footnotes

• Contributors The idea was conceived and originally drafted by FG. Redrafting of the work and addition of further intellectual content was done by NG. Both authors took part in revising the work and gave final approval for its submission. Both authors agree to be accountable for all aspects of the work.

• Funding This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.

• Competing interests None declared.

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