[xsl] Do xsl processors contain optimizer for conditions?

[cert21 <cert21@xxxxxxx>]

I know in many languages like Java and php when testing for multiple 
conditions
the engine is smart to return false when the first condition fails, so 
it does not even check
next conditions.
This saves some of the processing time.

I wonder if xsl engines follow the same logic, for example in test like 
this:

<xsl:when
               test="( (string-length($mystring) > 30)  and 
not(contains(substring($mystring, 1, 30), ' ') ) )">

If the string-length is < 30 then the second condition will not even be 
evaluated?