# Errors and User Control

The purpose of this activity is to explore the undo models used in single-user text editing. You will find a few different kinds of textboxes below. Experiment with your web browser's undo model for text editing by typing, deleting, changing properties, and using Undo. Try to figure out:

- how many undo streams are there—one, or many?
- how is the history divided into undoable units?
- how much previous state is recovered when you undo? (selections? cursor positions?)
- what visible feedback does Undo give? (e.g., if the Undo affects a location scrolled out of the box?)

## One line, plain text

## Multi-line, plain text

I never saw a Purple Cow, I never hope to see one. But I can tell you, anyhow, I'd rather see than be one.

## Multi-line, rich text

Reply (To The "Purple Cow")
by Gelett Burgess
Apres Cinq Ans,1914

Ah, yes, I wrote the "Purple Cow"--
I'm sorry, now, I wrote it!
But I can tell you anyhow,
I'll kill you if you quote it.