Underscore in php function

Question

What does it mean when a PHP function name begins with an underscore?

for example: __construct()

I know what the construct means but I've seen other places where the function begins with an underscore, or a double underscore and I'm just not sure of the significance.

Answer 1

It means that PHP calls it implicitly.

It's called a 'Magic Method'

Also, it's two underscores, not one.

Learn more here: PHP Magic Methods

Answer 2

In PHP, functions start with two underscores usually have special meanings. From the manual:

PHP reserves all function names starting with __ as magical. It is recommended that you do not use function names with __ in PHP unless you want some documented magic functionality.

For example __construct() is a special method which is called automatically while initializing an object.

Se also: http://php.net/manual/en/language.oop5.magic.php