l-compatibility">full compatibility</a>, just like making everything optional does. It is, however, less flexible than making everything optional.</p>
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<p>The idea, roughly, is that consumers with newer schemas can rely on the default values for missing required fields in older messages, much like optionality would have provided <code>null</code>. However, a major difference with optional fields is that default values are only used during reading, not writing. So, a writer can 