Text editing best practices (with tags, etc.)

I want to create a text field with some text, that is styled with tags. Think of MS Word, some ext is bold, some is a headline, etc. The tags that style the text are not visible to the user, he just sees the text in bold.

How do I preserve these tags? I mean when I backspace over the closing bold-tag, for example, how do I preserve that and prevent that the rest of the text is now bold until the end?

I guess this is a pretty basic question for experiences programmers. Are there any algorithms or best practices? This problem surely has been solved before, any pointers?

(If this is of any concern, I develop for the iPhone OS and the text field will be a UITextView, but my question is more general I guess.)

Thanks in advance!

Rather than thinking of the styles as open/close tags embedded in the text, think of them in terms of NSRanges and adjust them accordingly.

As of 3.2 you can use NSAttributesString. Even if you roll your own, it is a good reference.

An attribute is applied to a range of characters. When characters are added or removed, the ranges are adjusted accordingly.

Tags are for a flattened format like HTML or RTF. In memory during editing you need complex data structures like DOM or NSAttributedString.