r[lex.whitespace]
r[lex.whitespace.intro]
Whitespace is any non-empty string containing only characters that have the
Pattern_White_Space Unicode property, namely:
U+0009(horizontal tab,'\t')U+000A(line feed,'\n')U+000B(vertical tab)U+000C(form feed)U+000D(carriage return,'\r')U+0020(space,' ')U+0085(next line)U+200E(left-to-right mark)U+200F(right-to-left mark)U+2028(line separator)U+2029(paragraph separator)
r[lex.whitespace.token-sep] Rust is a "free-form" language, meaning that all forms of whitespace serve only to separate tokens in the grammar, and have no semantic significance.
r[lex.whitespace.replacement] A Rust program has identical meaning if each whitespace element is replaced with any other legal whitespace element, such as a single space character.