Is there a guideline for when to use != instead of (!condition) in PHP?
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Is there a rule or guideline for when to use `!=` instead of `(!condition)` when checking if a condition is true or false?

For instance, I have some pages that check if TLS is enabled before returning anything:

`if ($_SERVER['HTTPS'] !== 'on') { exit; }`

But I could also write it like this:

`if (!$_SERVER['HTTPS'] === 'on') { exit; }`

For some statements it seems cleanest to use the latter, for instance:

`if (!isset($_SESSION)) { session_start(); }`

... is shorter than the equivalent: 

`if (isset($_SESSION) == false) { session_start(); }`

Is there a standard or guideline for writing these statements, or is it just preference?

Note: I understand the difference between `==` and `===`, I just want to make sure my code is as clear and concise as possible.
