Document behaviour of built-in functions with complex criteria

See https://exceljet.net/formula/xlookup-with-complex-multiple-criteria
and https://groups.google.com/g/exceldna/c/bwXlP-OXfPM

If seems that a formula like
```
=XLOOKUP(1,(LEFT(B5:B16)="x")*(C5:C16="east")*NOT(MONTH(D5:D16)=4),B5:E16)
```
is evaluated differently in Dynamic-Array aware Excel vs older Excel.
In particular, the LEFT and MONTH functions don't return arrays to the formula in the older Excel, but instead only the interpolated row / column value.

It would be good to sort this out and document a bit.
Keywords would be "implicit intersection" and "dynamic arrays".