The mathematical functions like $add or $num interpret the passed string as an integer. The Python int conversion already ignores surrounding "normal" whitespace, such as an ASCII space or \t, but also some additional like thinspace '\u2009'.

But it does not trim some other characters that can be considered whitespace or invisible control characters that should maybe also ignored. Some to consider are:

• zero width space '\u200b'
• zero width no-break space '\ufeff'
• left-to-right mark '\u200e' and right-to-left mark '\u200f'