[development] += on arrays

[vlado]

> > "In addition to the basic assignment operator, there are "combined
> > operators" for all of the binary arithmetic and string operators that
> 
> Array is neither binary nor string. The relevant page is  
> http://www.php.net/manual/en/language.operators.array.php imo.
partially true - binary here means 2 arguments. Array is a built in type
and has a similar treatment to integer, string, ....

It is fair to say that the manual page should be explicit, rather that
use deductions, but hey, nobody's perfect.