Currier A and B

[Emma May Smith]

I don't know why the orthography would evolve. I'm seeking a model/process that fits the observation that the text changes over the course of the manuscript. Though the simplest reason for it would be that the script or language are new to being written, and the writer address problems as he finds them.

As to the nature of the changes, I'm not sure what the difference between evolution and stepwise would be here. Any orthography would be a set of discrete rules within the writer's head. Each one is either true or false at any given point in the manuscript. Multiple rules may have been changed at once, and some rules may have had a bigger effect than others.

I mean that if one reads a document in some language, then one naturally expects its orthography to be stable within this document. Are there are any real-life examples of books in a single language having their orthography evolving?

In medieval manuscripts you can't assume that the writer would even be self-consistent. A single writer may not have a stable orthography.