[FFmpeg-user] 'overlay' filter question

[Mark Filipak]

Here:
https://ffmpeg.org/ffmpeg-filters.html#overlay-1
is found this example:
ffmpeg -i input -i logo -filter_complex 'overlay=10:main_h-overlay_h-10' output
                                                  ^
What is ..................................... this?
It's not documented.

Thanks in advance,
Mark.