PHP's for loops are just like C's for loops. You can place arbitrary expressions 
in the initializer, test, and increment; do not put a call to a function in test:

	bad for performance (called N times):
			for ($i=0; $i < $b=complicated_function(); $i++)

	good for performance (called N times):
			for ($i=0,$b=complicated_function(); $i < $b; $i++)

There are two regular expression libraries that shipt with PHP: Posix and Perl-style.
Posix regular expressions are simpler, but often slower.
Perl-style regular expressions tend to be faster and are a lot more powerful -- but some find
them complex. But stick with the Perl-style regular expressions since these are the standard
in many other languages.

You often need to have arguments to your database queries, e.g.:

	SELECT title, pub_date, price FROM book WHERE book_id=3

this is fine functionally, but performance-wise, it is poor and can be dangerous:

- You must escape the arguments correctly (e.g., handle quotes)
- You prevent the database from performance some caching optimization on query compilation
- If the argument comes from the user, you may be leaving yourself open to a number of security
  vulnerabilities (SQL injection).
  
Bind the arguments to resolve the issue:

	$query= $conn->query("SELECT title, pub_date, price FROM book WHERE book_id=?", Array(2));
	if (DB::iserror($query)) {die ($query->getMessage());}

Parsing XML documents:

DOM 
	- easier to implement when re-noding a tree is required often
	- memory hog when doc size is large
SAX 
	- faster to process than DOM