Chapter 33. The Text Widget
Tk text widget is a general-purpose editable text widget with features for line spacing, justification, tags, marks, and embedded windows.
The Tk text widget is versatile, simple to use for basic text display and manipulation, and has many advanced features to support sophisticated applications. The line spacing and justification can be controlled on a line-by-line basis. Fonts, sizes, and colors are controlled with tags that apply to ranges of text. Edit operations use positional marks that keep track of locations in text, even as text is inserted and deleted.
Tags are the most important feature of the text widget. You can define attributes like font and justification for a tag. When that tag is applied to a range of text, the text uses those attributes. Text can pick up attributes from any number of tags, so you can compose different tags for justification, font, line spacing, and more. You can also define bindings for tags so that ranges of text can respond to the mouse. Any interesting application of the text widget uses tags extensively.