Controlling unwanted line breaks

It aids clarity to put style definitions on their own lines. However because the end of the line (the line feed) is outside the style, it is treated as part of the actual content, and appears in the result.

In HTML, whitespace is collapsed (except within regions such as  <pre>  </pre>  or the equivalent whitespace CSS) so generally this won't show up on the resulting HTML pages, assuming that's what aa_macro is being used for in the first place. Still, it doesn't look nice when looking at the actual HTML.

So aa_macro looks for lines that end in two spaces. When it sees them, it 'eats' both the two spaces, and the following linefeed. This allows definition of a style without anything appearing in the output.