In HTML, certain elements such as <ul> cannot have any text nodes in them, and any whitespace is ignored, see
A similar concept applies to OurBigBook, e.g.:
does not parse as:
but rather as:
because the content argument of ul is marked with remove_whitespace_children and automatically removes any whitespace children (such as a newline) as a result.
This also applies to consecutive sequences of auto_parent macro property macros, e.g.:
also does not include the newline between the list items.
The definition of whitespace is the same as the ASCII whitespace definition of HTML5: \r\n\f\t.