Be aware that when parsing yaml an unquoted Y value will become a boolean true

This may be desired or undesired behavior depending on context

- chr_name: X // becomes string X
- chr_name: Y // becomes boolean true

[
 [chr_name => X],
 [chr_name => true],
]

You definitely don't want chromosome Y becoming chromosome 1 (true) as happened to me, so heads up!

As Jesse Donat mentioned the type will be infered automatically. To enforce some type you can use the callback facility like this:

<?php
function cb_yaml_date($value, $tag, $flags) {
    return new DateTime($value);
}

$yaml = <<<YAML
event1:
  name: My Event
  date: !date 25.05.2001
YAML;

$ndocs = 0;
$data = yaml_parse($yaml, 0, $ndocs, array('!date' => 'cb_yaml_date'));

print_r($data);
?>

The above example will output something similar to:

    Array
    (
        [event1] => Array
            (
                [name] => My Event
                [date] => DateTime Object
                    (
                        [date] => 2001-05-25 00:00:00
                        [timezone_type] => 3
                        [timezone] => Europe/Berlin
                    )
    
            )
    
    )

BTW if you want to have large numbers you are probably using BC Math. Thus, you simple enclose your number in quotes:

<?php
$yaml = <<<YAML
largenumber: '14695760472279668267313200104308'
YAML;
?>

This is entirely dependent on type detection - as far as I can find there is no way to force a type and for instance when you have a very long integer as a value - in my case 1313035348823 it gets limited to 2147483647 - PHP's max integer.