All values should be undefined:
$a = [+ $a +] 
$b = [+ $b +] 
$c = [+ $c +] 
$d = [+ $d +] 
$e = [+ $e +] 
Here we will see an error:
[- $a = (qqqqqqqqqqqqqq -]
First of all assign a value:
[- $a = '(this is the value in $a)' -] 
Now we have some 'Umlaute':
[- $b = "$a äöü" -]
Second Error:
[+ $a+ +] [+ qq2$b +]
And now a and b together: [+ "$a$b" +]
Here we have some HTML tags within the perl code, Embperl will delete them! Ok. 
[+ $c = 
 6 + 17  * 3 +]
Embperl will also translate HMTL escapes to the right characters i.e. $a < 6 will get the perl expression $a < 6: 
[- $e = 2 -]
[+ $d = $e < 6 +]
Now they should have a value
[$if {$error is here ) $]
$a = [+ $a +] 
$b = [+ $b +] 
$c = [+ $c +] 
$d = [+ $d +] 
$e = [+ $e +] 
[$endif$]