$cfg["prepend"] defines a text (or # of tabs) to be prepended to the front of each HObfus obfuscation. Suppose you assign "I think, therefore I am." to $cfg["prepend"] like this.
$cfg["prepend"]="I think, therefore I am.";
Then HObfus will prepend "I think, therefore I am." to each HObfus obfuscation like shown below.
If you assign a number to $cfg["prepend"], then the same number of tabs will be prepended to each HObfus obfuscation. For example, in the following setting, 25 tabs will be prepended.
$cfg["prepend"]=25;
If you do not want to prepend any text or tabs, then set $cfg["prepend"] to an empty string like this.
$cfg["prepend"]="";
The default value of $cfg["prepend"] is 100, which prepends 100 tabs to each HObfus obfuscation.
$cfg["prepend"]=100;