Word processors (e.g. Microsoft Word) display documents to the user as styled text. The user can select a part of this text and apply styles to it, and edit the text.
The word processor must (I guess) have an internal representation of the document that indicates which bits of the text displayed to the user should be styled differently. But the user doesn't interact with this internal representation. They interact with the text, by using the caret and selecting portions of it.
What data structure might the word processor use to efficiently map the text with which the user interacts to its internal model of the document?
Best Answer
There are an infinite number of ways to do it, but the basic concept isn't that hard. Say you used html for your internal representation:
If your GUI widget tells you the cursor is after the 4th character, all you have to do is count to the 4th character, but when you come to something inside angle brackets, you don't count it, but instead keep track of what formatting it is applying or unapplying.
Obviously, for a large document you don't want to count characters from the beginning every time you press a key, so they use more efficient data structures, but the basic concept is the same. You have some sort of mapping between visible characters and their metadata.