This is the same issue as https://jira.ixsystems.com/browse/NAS-103463 however since its a different page and differnet JS code I felt it would be best tracked by another ticket.
The name for a Boot environment does not allow special characters which is good, however there is no UI element to tell a user what values are not allowed. If you attempt to enter a name of:
for example, it will fail, the field will turn red and you will not be able to save.
There should be a UI text field that also shows up and informs the user of what characters are allowed.
A new user of FreeNAS that is not familiar with FreeBSD Boot Environments and how they work may not know what characters are allowed, so this would be an easy thing to help improve new user experience.