It would be a welcome addition if error messages could be displayed with a
user-friendly field name that matches the field's label.

Now a field error with field id "my_field" is displayed in the error handler
instead of the more user-friendly label "My Field".

Possibly, one could have the option to add an attribute to the field, e.g.
something like data-smtfm-errorlabel="My Field", so that one can control how
errors are displayed.