Purpose: Evaluates the operands from left to right and returns the first one which is declared and not null.

Return Values: Returns null if all operands are null or not declared, otherwise the value which is declared and not null.

Example:

heitml input:	resulting output:
<? default (null,5,7)>	5
<? default (null,ff.x.y.z,null) "Nn">	null