I can give you some feedback since I tend to write a lot of PHP.

Mostly, code style is about consistency. You can have infinite arguments about whether opening braces should go on the same line as the operator/function, but at the end of the day as long as you stay consistent it doesn't really matter.

Here are some consistency issues I found. Your function declarations put the opening brace on the following line, but flow controls open on the same lines. Ex: https://github.com/EGreg/Platform/blob/master/platform/plugi...

In the same vein, commenting seems inconsistent - this file's docblock opens with /* */ style comments, but then you switch to // style. Ex: https://github.com/EGreg/Platform/blob/master/platform/Q.php...

Further down, you use two styles of if(), one with braces and one without, right next to each other: https://github.com/EGreg/Platform/blob/master/platform/Q.php...

I much prefer 2 space indents to tabs. To me, it's much more readable. I noticed your HTML output is also tabbed, which (arguably) needlessly increases the horizontal width you need to see a page of code, especially with modern deeply-nested structures.

Overall the project looks well thought out, and you may have valid reasons for any/all of the above. Just throwing in my initial reactions as a project outsider.

Also, dunno if you know about PSR, but here it's a good starting point that many people (potential contributors) are familiar with: http://www.php-fig.org/psr/psr-2/

Thanks for the reference! PSR-2 looks useful.

I guess I wanted to know more feedback about the design and architecture of the system, the names for things etc.

There's a bunch of directories where you keep the PHP and JS files in the same directory, like this one: https://github.com/EGreg/Platform/tree/master/platform/plugi...

Any special rationale behind that approach?