The characters to be appended should be valid Unicode characters as
described in Unicode Character
Representation. Note that supplementary characters may be composed of
multiple 16-bit char values.
Appendables are not necessarily safe for multithreaded access. Thread
safety is the responsibility of classes that extend and implement this
Since this interface may be implemented by existing classes
with different styles of error handling there is no guarantee that
errors will be propagated to the invoker.