The following table contains a list of whitespace characters that MongoDB removes by default when using the $trim, $ltrim, and $rtrim aggregation pipeline operators.

Unicode	Escape sequence	Description
U+0000	‘0’	Null character
U+0020	‘ ‘	Space
U+0009	‘t’	Horizontal tab
U+000A	‘n’	Line feed/new line
U+000B	‘v’	Vertical tab
U+000C	‘f’	Form feed
U+000D	‘r’	Carriage return
U+00A0		Non-breaking space
U+1680		Ogham space mark
U+2000		En quad
U+2001		Em quad
U+2002		En space
U+2003		Em space
U+2004		Three-per-em space
U+2005		Four-per-em space
U+2006		Six-per-em space
U+2007		Figure space
U+2008		Punctuation space
U+2009		Thin space
U+200A		Hair space

The above characters are removed by default when using the $trim, $ltrim, and $rtrim operators. However, you can alternatively use the chars parameter to specify which characters to remove when using those operators.