The quality or state of being extensible; the degree to which something can be extended or stretched.
From 'extensible' plus '-ness', a straightforward adjective-to-noun transformation using the Germanic suffix pattern.
While technically correct, this word is rarely used because 'extensibility' does the same job more elegantly—it's a reminder that English often has both '-ness' and '-ity' options, with '-ity' often winning out for Latin-based words!
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