HAML's eating the white space can be "%span><=", but not "><="?

Question

I have used

%span><=

and it can eat up the white space between this line and the next, and also outside of the span tag, but it seems like an element needs to be used. The form

><=

or

<=

or

>=

can't be used to eat the space. Or is there some ways to make them work?

some docs at:
http://haml-lang.com/docs/yardoc/file.HAML_REFERENCE.html#whitespace_removal_and