Word count is important because it influences A) the amount of time copyeditors should spend improving your manuscript, and B) the amount of time it takes JMIR staff to typeset your article. As of February 27, 2018, fees for additional editorial work may be applied to papers which are considered excessively long (over 5000 words).
Word count does include:
✔ Manuscript body
✔ Text-focused tables
✔ Table captions
✔ Figure captions
✔ Acknowledgements section
✔ Authors' Contributions section
✔ Conflicts of Interest statement
Word count does not include:
✘ Author metadata (names, affiliations, addresses, etc)
✘ Data-heavy tables
✘ Multimedia Appendices
Inclusion/exclusion of elements is directly based on what the copyeditor needs to address.