Make text in ZPL label bold or underlined?

Question

Due to a new EU law every food packaging label has to outline possible allergy-causing ingredients by either styling them bold or underlined in the ingredients

Answer 1

To underline - use a monospaced font like AA,AC,AD,AF or AG

Use

^FO350,50^AGR^FDwhatever,milk,butter,salt^FS
^FO340,50^AGR^FD         ____ ______^FS

where the underline here is under milk and butter, you can adjust the offset by trimming the FO's X and Y positions by a few dots (10 X here)

On further investigation, I found

To bold

Use an old dot-matrix-printer trick. Still using fixed-pitch font, reprint the text but replacing the non-bold characters with spaces and adjust the X-position by 1 or 2 dots, reprint again with the Y-position adjusted by 1 o2 2 dots.

^FO350,50^AGR^FDwhatever,milk,butter,salt^FS
^FO348,50^AGR^FD         milk butter^FS
^FO350,52^AGR^FD         milk butter^FS

To underline, draw a graphics box below the required letters. This is relatively easy to calculate since the width of each letter is constant.

^FO345,490^GB0,160,4^FS
^FO345,690^GB0,240,4^FS

I tested using an A300 and 8"*3" labels, so I needed to rotate the text, hence some odd calculations. The manual does not show the ^FS, even in the examples but I found it was required.