This is an Emacs question.
Occasionally I want to type something in boldface, to draw attention to it. So I use the command M-o b, and type, and it's in bold. Then I use the command M-o d, and type, and it's not in bold. That's what I want, a word in bold that stands out from standard text. Looks good. I save the file. When I re-open it, the bold is gone. Where'd it go?
Is this question related to a specific O'Reilly title? If not then unfortunately I wont be able to assist as I can't provide support of this nature. I would suggest searching for a forum on Emacs posting your question there might result in better assistance.