The following codes work in all three modes:
$c
number of currently selected objects
$C
total number of objects in folder
$sX
total size of selected objects
$SX
total size of folder content
$fX
free space on the folder's drive
$zX
total size of the folder's drive

In the above four, X is a special format specifier character.

$x(xxx)
Left-oriented tabulator: print the following information at X position "xxx" (relative to the left border of the status bar).
Example: $x(300)$sK will always print the total size of the selected objects at X position 300.
$x(-xxx)
like before, but relative to the right border of the status bar.
Example: $x(-150)$sK will print the total size of the selected objects at X position 100, if the status bar is currently 250 pixels wide.
$x(xx%)
like before, but the X position will be calculated using "xx" as a percentage relative to the current width of the status bar.
Example: $x(50%)$sK will always print the total size of the selected objects in the center of the status bar.