The notransform filter takes one argument, a filter F:
  notransform a4
  notransform player white "Kasparov"

The value of notransform F in the current position is the same as the value of F in the current position.

If T is a transform filter, such as flip, shift and so on, then the value of

  T notransform F 

is the same as the value of

  notransform F

In other words, notransform nullifies the effect of any enclosing transform.

The notransform filter is primarily useful in certain functions and also for debugging. For example, the passedpawns filter is defined internally as:

   P&~down horizontal 0 1 p}

This ensures that

  rotate90 passedpawns  passedpawns

Otherwise, the rotate90 would modify the down and horizontal direction filters and odd results would obtain. Note that the flipcolor transform inside the notransform filter operates as usual.