Whitespace depends on the context. For example, you could have characters that are not counted as whitespace in Unicode, but end up rendering as whitespace when displayed in a particular context. The only real way to check for this is to actually try to render it and see what happens. There are some other ways to approximate it, like checking the font that you use for rendering, or the bounds of the glyph, or other things like that, but the only way to really know for sure in all cases is to just render it and see what happens.