One of the greatest advantages digital content provides is its immediate malleability. With the right software changes can be made quickly and globally. A hallmark of this flexibility is the great big undo\/redo stack that nearly every piece of software maintains.<\/p>\n
An application normally implements undo by recording inverse operations for every action the user takes. For instance, to undo adding 10 to a particular number, you simply subtract 10. When a user deletes a word from a document, the inverse operation is to simply insert that same word back in.<\/p>\n
Looking more closely at the requirements necessary to undo the deletion of a word, you can see that you need to know not only what the word was, but where the word was located in the document. At a lower level this location is simply the number of characters that preceed the deleted word. <\/p>\n
For instance, imagine a document containing only the text “ice is blue”. Note that the word “blue” is preceded by a total of 7 characters. So to undo the deletion of the word “blue” from the document, we simply insert the word “blue” after the 7th character in the document.<\/p>\n
Locations are complicated by document content that automatically updates itself. One example might be a timestamp. One second the stamp could read “Thursday 23:59”, the next, “Friday 00:00”. You can see that the stamp shrunk by 2 characters. Had our imaginary document in the previous paragraph contained a timestamp such as this one, the location we need to reinsert the word “blue” at to undo the deletion would have changed. To accommodate undo after a timestamp we need to be able to describe locations in the document like “the 7th character after the 2nd timestamp”.<\/p>\n","protected":false},"excerpt":{"rendered":"
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