GDOv7 Philosophy

Everything is a string in the beginning. Do not convert unnecessarily and do it lazily. Sadly type annotations force a bit of conversion.
No code duplication. Re-use as much as possible. Validator inheritance and js bridge is noteworthy.
No redundant information. I don't need to annotate in three ways that this is a string. Never is bad, one time is great, three times is sad.
Consistency. Mostly, always?, There is one way to things. Do them this way and as good as you can.
Less is more. there are no getters, just public attributes. Setters have the same name and allow chaining. This pattern is used across the whole project.
Aggressive programming! not defensive. Do not check for null values or anything. If there is a problem, a helpful error has to be shown automatically!
A method should fit on a screen. A file should have not more than 300 lines. Of course that's not always feasible, like GDO.php has almost 2000 lines of code. Those huge classes are very rare in GDOv7.
Do things the right and easy way. KISS* :) If Something does not work right away, maybe come back later. Of course you have to try things first.
No external resources unless really wanted. No production libraries during development, all src of everything.

GDOv7 Philosophy: Public attribute pattern

Here is an example of how this code pattern looks like.

public string $label = 'test';
public function label(string $label) : self
{
    $this->label = $label;
    return $this;
}

This way you can chain setters like GDT_String::make()->label('hi')->max(32)->ascii()->caseSensitive(true)

GDT are plugged together with many traits. A complete list of traits is available here.

I really rarely had to write some stupid validator for a long time.

FileUtil isFile() checks readability. (@TODO)

Directories always end with a trailing slash on all platforms. I wished windows would switch to / as well -.-