Validate on submit:
- https://johnnycode.com/2014/03/27/using-jquery-validate-plugin-html5-data-attribute-rules/
- https://jqueryvalidation.org/validate/#highlight
- https://jqueryvalidation.org/reference/#link-markup-recommendations
- https://stackoverflow.com/questions/14962973/validation-rules-applied-to-all-elements#24812910
- https://jqueryvalidation.org/validate/#errorplacement
- https://stackoverflow.com/a/15195924/6850747
- https://jqueryvalidation.org/valid/
- https://dev.recurly.com/docs/events
- https://stackoverflow.com/questions/21699709/combining-custom-error-placement-with-success-is-not-working-jquery-validate-plu#21733576