Purpose: Checks whether a value is of type Boolean. The value can be of any type but must be declared in case of a variable or object field.

Return Values: Returns true if and only if value is of type Boolean, otherwise false.

Example:

heitml input:	resulting output:
<? isbool("string")>	false
<? isbool(3)>	false
<? isbool(true)>	true
<? isbool(emptytuple)>	false