Programmatically query or modify the cells in a notebook.

To Extract Information from Cells...

Get the contents of all the text cells in a notebook:

Out[1]=

To Modify Cell Styling...

Add a dingbat to all Section cells in a notebook. nb is set to the NotebookObject of the target notebook (see Find a Notebooks NotebookObject Identifier):

To Edit Cell Contents...

Change every instance of a in a text cell to x: