~TiddlyWiki's display is driven by an underlying collection of <<.def widgets>>. These are organised into a tree structure: each widget has a parent widget and zero or more child widgets.
~TiddlyWiki generates this <<.def "widget tree">> by parsing the ~WikiText of tiddlers. Each component of the ~WikiText syntax, including even the trivial case of ordinary text, generates a corresponding widget. The widget tree is an intermediate representation that is subsequently rendered into the actual display.
Each class of widget contributes a specific ability to the overall functionality, such as the ability to <<.wlink2 "display an image" ImageWidget>> or <<.wlink2 "a button" ButtonWidget>>, to <<.wlink2 "call a macro" MacroCallWidget>> or <<.wlink2 "transclude text from elsewhere" TranscludeWidget>>, or to [[mark a piece of text as a heading|HTML in WikiText]].
The more specialised widgets use a general-purpose [[widget syntax|Widgets in WikiText]] as their only possible WikiText representation.
The following classes of widget are built into the core:
