Steps to reproduce the issue

Create a form including a subform.

Include the following setting (as per Joomla standard form field documentation):

validate="SubForm"

Expected result

Subform works.

Actual result

Get error message:

Joomla\CMS\Form\Field\SubformField::validate() rule SubForm missing.

System information (as much as possible)

Works on Windows server, not Linux

Additional comments

https://docs.joomla.org/Subform_form_field_type

The field property needs to be in lower case - the documentation says it is case sensitive but the given value (SubForm) is wrong. It should be:

validate="subform"

Documentation needs correcting.

Even better should the FormHelper::loadRuleType($type) method convert it to lower case regardless?
Impact of doing that on existing usages, including 3rd extensions?