PanModal: Better support for thumb accessibility on Slack mobile

This post details the technical implementation of PanModal, a custom iOS modal transition library. It explains the use of UIKit's UIViewControllerTransitioning API, including delegates, animators, and presentation controllers, to create a draggable modal. The post highlights challenges with gesture recognition when integrating with child UIScrollView components and the solution using KVO to manage scroll offset changes. It also discusses the design goals of creating a simple, robust API that supports any UIViewController subclass and maintains 60 FPS performance.