On this website, we use the tilde character (∼) in the $\mathrm{\TeX}$ sense of the term, as a non-breakable space. When we do need to display a tilde, we use the U+007E character (∼ again). Most of the time this does not need worry you, but until we fix this escape sequence in code blocks, you'll need to replace manually the Unicode version by the proper ASCII one for if you copy/paste from us.