Ok first off apologies if this seems like a silly question but I'm actually having a hard time finding the answer, even on Ellislab's website and Google.
In ExpressionEngine 2.x it used Codeigniter as the framework. There was a directory containing the framework files and you could use features of Codeigniter within EE projects.
I'm just building a site on EE 3.3.1 and can't see any such directory in 'system' or it's subdirectories. Is there an underlying framework that can be used?
The reason I ask is because a lot of plugins don't seem to have been updated for EE 3.x compatability. I'm wanting to develop something to send an email and in 2.x I would have used Codeiginters features to do this.
So, is EE 3.x using Codeigniter and if not is there a framework that can be accessed, e.g. by using PHP in templates and then getting an instance of the framework?
Edit (15 Nov 2016) - this post seems quite frequently viewed. If anyone has any examples or information about how they've written custom PHP on an ExpressionEngine 3.x site please post it as an answer. The lack of a documented framework, or having to rely on one that might get removed, is a major issue for anyone doing custom PHP development on EE 3.x sites. Ellislab should really comment on this.