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tickbox variable: $complexvalflag -- real/cplx data
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keyboard equiv: <none>

The "cpx" tickbox at the upper middle (under SEND
PNT) is normally autoset on read real or complex
overlay data with tkmedit command line arguments:

  -real <format>
  -complex <cformat_r> <cformat_i>

This flag toggles between expecting real-valued
data and complex-valued data.

It also affects how the filename argument in the
"valn:" (or "valnup:") entry is treated .  If
complexvalflag is set, a "R" on the "valn:" entry
line will attempt to read a pair of files.  An _r
(or _x) infix will result in an attempt to also
read a matching file with an _i (or _y) infix.
