All good formats -- text or binary -- are capable of being extended over time in a backwards-compatible way, in order to fix mistakes. Formats that don't allow

All good formats -- text or binary -- are capable of being extended over time in a backwards-compatible way, in order to fix mistakes. Formats that don't allow this are bad and should not be used. Protobufs and Cap'n Proto in particular have very strong support for forwards- and backwards-compatibility. Choosing a too-small fixed integer size is one way that a format can screw up and need correction -- one which happens to be (somewhat) exclusive to binary formats. But there are plenty of ways text formats can screw up too, like trying to pack fundamentally structured data into an ad-hoc hard-to-parse string format in order to make it look more pleasant to humans (I'm looking at you, MIME type specifications), or failing to use consistent parsing rules (cookie and user-agent headers totally flout otherwise-consistent HTTP grammar rules, confounding well-written parsers).