\obeywhitespace makes both end-of-lines and space characters in
the input be respected in the output. Unlike plain TeX's
\obeyspaces, even spaces at the beginnings of lines turn into
blank space.
By default, the size of the space that is produced by a space
character is the natural space of the current font, i.e.,
what \ produces.
Ordinarily, a blank line in the input produces as much blank vertical
space as a line of text would occupy. You can adjust this by assigning
to the parameter \blanklineskipamount:
if you set this negative, the space produced by a blank line will be
smaller; if positive, larger.
Tabs are not affected by this routine. In particular, if tabs occur at the beginning of a line, they will disappear. (If you are trying to make TeX do the "right thing" with tabs, don't. Use a utility program like expand instead.)