(View the source of this document to see how the hard line breaks are being controlled).
By default, newlines between consecutive lines in prose (i.e., paragraph text) are not preserved. They are treated as a single space, just like in HTML.
first line second line third line
If you want newlines to be preserved as hard line breaks, you can add the hardbreaks option to the paragraph.
first line
second line
third line
If you want to set this option globally, define the hardbreaks attribute in the document header (but know what you are doing).
A third option is to add explicit hard line breaks in the source by adding a space followed by a plus to the end of the line.
first line
second line
third line
Newlines are always preserved in preformatted blocks, such as a literal paragraph, literal block, or listing block.
first line second line third line