Some things would be easier if certain public HTTP-based APIs supported a (custom) APPEND HTTP-method.
To let users append to an existing file.
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PUT is inefficient for this use case.
PATCH and POST already exist, but what they support is much more generic than this. It is the same way that you could use POST instead of DELETE, PATCH, and PUT; but it is simpler in some ways if you use a separate method for each pattern.