HTML Living Standard specifies 5 characters as the ASCII whitespace: U+0009 TAB, U+000A LF, U+000C FF, U+000D CR, and U+0020 SPACE. In the form of text, they are treated as normal space characters and sequential whitespaces are collapsed as a single space in many cases (this behavior can be changed by the
white-space CSS property). They are also used as a separator of an element name and its parameters, class names, and so on.
ECMAScript® 2015 Language Specification specifies several Unicode codepoints as white space: U+0009 CHARACTER TABULATION <TAB>, U+000B LINE TABULATION <VT>, U+000C FORM FEED <FF>, U+0020 SPACE <SP>, U+00A0 NO-BREAK SPACE <NBSP>, U+FEFF ZERO WIDTH NO-BREAK SPACE <ZWNBSP> and Other category “Zs” Any other Unicode “Separator, space” code point <USP>. These characters are usually unnecessary for the functionality of the code.