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variable: $revphaseflag -- reverse time axis
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default: 0 (FALSE)

The "rev" tickbox (lower right) reverses the
phase of complex-valued color scales (it also
reverses the sign of the "BW" color scale).

This happens *before* adjustment by angle_offset.

For Fourier-analyzed data, when $revphaseflag is
1 ("rev" is ticked), the time axis is effectively
reversed, that is, f(t) -> f(-t).

In general, this is not equivalent to multiplying
by -1 ($invphaseflag).
