Describes API for getting current position in a stream, writer, or underlying file.
The expected functionality is simple: if you are a output stream / writer, and you've written 50 bytes to the stream, then
should return 50; if you are an input stream or file reader, and you've read 25 bytes from the object, then it
should return 25.
In the context of an iterator or any producer-like object that doesn't map directly to a byte stream,
return the position (in the underlying stream being read/written to) of the most-recently read/written element. For example, if you
are reading lines from a file with a
should return the byte position
of the start of the most recent line returned by