internal?

        # IO::Buffer.internal?

(from ruby core)
### Implementation from Buffer
---
    internal? -> true or false

---

If the buffer is *internal*, meaning it references memory allocated by
the buffer itself.

An internal buffer is not associated with any external memory (e.g.
string) or file mapping.

Internal buffers are created using ::new and is the default when the
requested size is less than the IO::Buffer::PAGE_SIZE and it was not
requested to be mapped on creation.

Internal buffers can be resized, and such an operation will typically
invalidate all slices, but not always.