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Changes between Initial Version and Version 2 of Ticket #62604

-                      initial
+                      v2
 Related: https://github.com/WP-API/docs/issues/194
 ```php
+{{{#!php
 'type' => 'string',
 'validate_callback' => function( $should_be_date ) {
      return preg_match( '/^\d{4}-\d{2}-\d{2}$/u', $should_be_date );
+}
+```
+}}}
 Above validation expects the parameter should be 'YYYY-MM-DD' format, but actually any string as "valid" because `preg_match()` returns 0(falsy value) for mismatch.