The classes, functions and types, grouped by what they are for.

[detail level 12]

Application	GUIApplication, the frame, GUIContent and event handlers
Controls	Every control by family, and the types they take and return
Windows and layout	Windows, horizontal and vertical groups, areas, scroll bars, caching, label and button groups
Text and images	Text, labels, drag labels, selectable text and images
Buttons and toggles	Buttons, command buttons, toggles, switches and checkboxes
Fields	Text, search, autocomplete, numeric, vector and typed fields, dropdowns, lists and dictionaries
Sliders	Sliders with and without a value field
Color and gradient fields	Color and gradient fields with their picker popups
Lists and reorderable groups	List views and drag-to-reorder groups
Tables, trees and grids	Columns, sorting, selection and data sources for tables, tree views and grid views
Tabs, docking and toolbars	Tab bars, dock nodes, dock layouts, documents, toolbars and the toolbar dock
Menus, tooltips and dialogs	Menus, context menus, the menu and title bar, tooltips, message dialogs and toasts
Node view	Nodes, pins and links for the node graph editor
Other controls	Breadcrumb, status bar, command search and the settings panel
Layout	Flexbox and grid layout, constraints and units
Styling	Themes, styles, colors and gradients
Text	Shaping, fonts, text atlases, numeric text and the clipboard
Input	Input state, handlers, commands, shortcuts and undo history
Elements and state	IDs, element storage and the state kept between frames
Graphics	The graphics backend interface, renderer, images and custom drawing
Vulkan backend	The Vulkan graphics backend, and sharing a host's device and images
Windows and platform	Window backends (SDL, null, image), OS windows and window flags
Diagnostics and memory	Logging, the profiler and allocation hooks
Utilities	Base types, results, hashing, JSON and number parsing