This information is part of the Modelica Standard Library maintained by the Modelica Association.

This block is a synchronous version of Modelica.Blocks.Math.BooleanChange. It uses previous instead of the implicit pre of change to set the Boolean output y to true when the boolean input u changed. Thus, it's logic is:

if firstTick() then
  y = false;
else
  y = not (u == previous(u));
end if;

This block might be superfluous and replaced by Modelica.Blocks.Math.BooleanChange when the semantics of change are relaxed and well-defined for clocked discrete-time partitions.