This will enable or disable symbolic mode of the current cell. It
differs from ShowSymbolic in two ways. First, it applies only
to cells with a symbolic representation, meaning that it has a
symbolic form which may or may not be visible. Second, it will change
the status of a flag in the cell, but there will be no updating of the
screen or other internal things (such as undo logging). The caller
must reset to the original state before a screen redisplay or any
major operation. This is much faster than calling ShowSymbolic,
and can be used when making quick changes to a cell.
The return value is 1 if the current cell was previously actively
symbolic, 0 otherwise. In physical mode the return value is always 0
and the function has no effect.