Source Highlighting
An easy way to spot very basic errors is to use a text editor that has syntax highlighting capabilities. Editors like these will recognize that you are editing a PHP script and automatically highlight the text in such a way as to make each element stand out in the source code. We discussed syntax highlighting earlier, but what I want to mention here is that PHP has built-in support for syntax highlighting itself.
The two key functions here are highlight_file() and highlight_string(), although there is also a function show_source() that is an alias to highlight_file(). This takes a filename as its parameter and outputs that file to the screen, with all keywords, strings, numbers, and functions highlighted in various colors, as shown in Figure 22-1. The highlight_string() function is almost identical, except it takes a string as its parameter.
Warning
Many people use these two functions to allow visitors to their site to view the source code for their pages. However, it is important to remember that doing so potentially reveals secret information, such as database passwords.

Figure 22-1. PHP has its own syntax highlighting system that provides a little help for debugging, but is still no replacement for full syntax highlighting
This example shows how to highlight a string of code and also a file:
$mystr = '<?php $foo = "bar"; $bar = array("baz", "wombat", "foo"); var_dump($foo); ...