Say, when you have a fair amount of text that you need to alt. (I realize it's best to pull it out of an image and into plain text, if possible ... but things aren't always ideal, unfortunately ... and when they're not, it'd be good to have a consistent, reliable approach.)
Sometimes you want to emphasize a headline, line breaks, etc.
I'm thinking for best reading by both humans (using screen readers, etc.) and also search engines. Optimizing for sighted humans is simple enough -- one can use asterisks, or other visual punctuation, whitespace, etc. ...
** HEADLINE ** I would really like to know how to properly *emphasize* things in alt-texts. And how about line breaks and whitespace? <Latest specials are here>
But how does that come across to search engines? To screen readers? Is there a best practice regarding this type of thing, a common language of conventions that people/Google understand?