2a.
italics. use surrounding underlines to indicate italics.
if you are only emphasizing one word, they go before and after.
if you're emphasizing a string of words, place the underbars before and after, and use one to replace each space in the string.
if you have linebreaks in your text, the surrounding underbars
should be ended at each linebreak and then start anew again
at the beginning of the next line.
2b.
bold. use surrounding asterisks to indicate bold.
you should note that headers should not be indicated as bold.
(it's up to the end-user to decide how the headers are displayed.)
2c.
bold italics. use /surrounding/slashes/ for bold italics.
2d.
other emphasis. you can specify other types of emphasis.
~any~ non-numeric from the top row of a qwerty-keyboard can be used to indicate such a different manner of emphasis; use it to ~surround~the~word~or~phrase~ in the usual way.
you should inform the person reading your text at the outset what this special emphasis is intended to convey to them.
(note: this next part is the one where the rule isn't concrete yet.)
then, so the zml-viewer-program displays it as you would like, you should also put the display instructions with the character. for example, let's say that, for the tilda character used above, you wanted the zml-viewer-program to display it in green italics; the first or last tilda in your text should be around ~green~italics~. (a set of terms that the viewer-app recognizes will be formulated.)