Syntax clarification

[netfrugal]

I'm about to feel really unintelligent for asking this, since I'm sure this is a most likely a basic thing to know.

What is this? " => "

I see it in many instances, for example:

<?php

$registered_types = array(
    "application/x-gzip-compressed"     => ".tar.gz, .tgz",
    "application/x-zip-compressed"         => ".zip",
    "application/x-tar"            => ".tar",
    "text/plain"                => ".html, .php, .txt, .inc (etc)",
    "image/bmp"                 => ".bmp, .ico",
    "image/gif"                 => ".gif",
    "image/pjpeg"                => ".jpg, .jpeg",
    "image/jpeg"                => ".jpg, .jpeg",
    "application/x-shockwave-flash"     => ".swf",
    "application/msword"            => ".doc",
    "application/vnd.ms-excel"        => ".xls",
    "application/octet-stream"        => ".exe, .fla (etc)"
); # these are only a few examples, you can add as many as you like

?>

Is it similar to the equals (=) sign? or the double equals (==) sign?

[YAOMK]

the => operator is used to associate key/value pairs in associative arrays.

In your example: "application/x-gzip-compressed" is a key and its value is ".tar.gz, .tgz".

[Weedpacket]

(See, for example, the manual page for array).