HTML5 in Safari 9.0.1 (11601.2.7.2) - `html5test.com
Safari does support HTML5 and does support form validation, however support for 'required' in Safari on OS X and iOS is 'partial'.


  Partial support refers to lack of notice when form with required fields is attempted to be submitted.


Source: caniuse.com/#search=required

Implementation is off-topic here, but feel free to search for solutions on Stack Overflow.