Purpose: Computes the length of a value. The value parameter must be string or an object.

Return Values: Returns the length of a string if value is a string or the number of object fields if value is an object.

Example:

heitml input:	resulting output:
<? len("text")>	4
<let x="Hello World"; ? len(x)>	11
<? len(emptytuple)>	0
<let x=emptytuple;x.f1=1;x.f2=2; ? len(x)>	2
<let x=array(2);? len(x)>	2