Possible ways:
...
or
style=\"white-space:pre\"
Anything else?
Try .
As per the documentation at Special Characters:
The character entities
anddenote an en space and an em space respectively, where an en space is half the point size and an em space is equal to the point size of the current font. For fixed pitch fonts, the user agent can treat the en space as being equivalent to A space character, and the em space as being equivalent to two space characters.