Email input field on Event Registration and Online Contribution pages does not do basic email format validation

I can enter invalid email address strings like this in the Email Address field in Event Registration or Online Contribution:

"dave@foobar.org,dave@example.org"
"davefoobar.org"

... and we don't throw a formRule error, and we do save these values to the civicrm_email record. However, if I go to Edit Contact and try to save a record with these values, we throw the expected "Email is not valid." error.

NOTE: Someone registered for a meetup with "two emails" like the above a while ago - and when I tried to send a reminder email to registered participants - I got an error (expected). This is an example of how this issue can cause problems.