It isn't just the usual non-breaking space. I've seen other space types like "En Space" creep into content copied into HTML entry forms, and cause issues further down the line (usually a ? appearing when an app tries to convert to a non-unicode encoding and doesn't understand these characters).<p>There are a few spaces in the Unicode standard:
<a href="https://www.compart.com/en/unicode/category/Zs" rel="nofollow">https://www.compart.com/en/unicode/category/Zs</a><p>And the list linked above doesn't include things like zero-width-joiner. See <a href="https://en.wikipedia.org/wiki/Whitespace_character" rel="nofollow">https://en.wikipedia.org/wiki/Whitespace_character</a> for a fuller list.<p>If you want to be evil to a programmer, as well as being tricksy with white-space, replace some semi colon characters (U+003B - ;) with Greek question marks (U+037E - ;) and see ho wlong it takes them to work out why their compiler or linter isn't happy…<p>The takeaway from all this is that you should never assume plain text is simple.