I finally logged in ... (facepalm) ... in case the question comes up, $TK{'vl'} is a Tk::Frame which is "view left" or 'vl' in the Tk GUI I'm building. Or trying to build. Or failing at. It depends on your point of view, and visual acuity.

# Create a left hand view frame in the workspace frame - for the tree
$TK{'vl'}=$TK{'ws'}->Frame()->pack(-side   => 'left',
                                   -anchor => 'n',
                                   -expand => 0,
                                   -fill   => 'both');
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Similarly 'ws' is a workspace Tk::Frame inside the main window. But that's probably not important.

I create a button to report the tree xview value and just was lost even more ...

  my @pos=$TK{'perltree'}->xview();

  my $pos=shift(@pos);

  print 'xview=' . join(",", $pos) . "\n";
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Thanks from nzsvz9