LOC( [#]fnbr )
For a file on the Flash Filesystem or SD Card opened as fnbr this will return
the current position of the read/write pointer in the file. Note that the first byte
in a file is numbered 1.
For a serial communications port opened as fnbr this function will return the
number of bytes received and waiting in the receive buffer to be read. #0 can
be used which refers to the console's input buffer.
The # is optional.