Till now we have used a static variable/getter/setter to decide what type of result should be returned when a formula is evaluated and an array is the result. This is messy; it would be much better to use an instance variable instead. We cannot eliminate `setArrayReturnType` and `getArrayReturnType` because that would be a BC break. I am considering whether they should be deprecated. In the meantime, I have added a new instance property `instanceArrayReturnType` with getter and setter methods. The property is initially null, and, if it remains so when needed, the static property will be used instead. However, if it is set, its value will be used.
Implement SPILL for dynamic arrays. Calculating a dynamic array function will result in a SPILL error if it attempts to overlay a non-null cell which was not part of its previous calculation. Furthermore, it will set to null all cells which were part of its previous calculation but which are not part of the current one (i.e. one or both of the dimensions of the calculation is smaller than it had been); this should also apply for spills (whose result is reduced to 1*1).
Excel will stop you from changing the value in any cell in a dynamic array except the formula cell itself. I have not built this particular aspect into PhpSpreadsheet.
As usual, MS has taken some unusual steps here. If the result of a dynamic array calculation is #SPILL!, it will nevertheless be written to the xml as #VALUE!. It recognizes this situation by adding a new `vm` attribute to the cell, and expanding metadata.xml to recognize this.
A new optional parameter `$reduceArrays` is added to `toArray` and related functions. This will reduce a dynamic array to its first cell, which seems more useful than outputing it as an array (default).
oleibman