Node:fwd-para within paragraph, Next:, Previous:fwd-para between paragraphs, Up:forward-paragraph

Within paragraphs

The next expression in the outer while loop is an if expression. The Lisp interpreter evaluates the then-part of the if when the fill-prefix-regexp variable has a value other than nil, and it evaluates the else-part when the value of if fill-prefix-regexp is nil, that is, when there is no fill prefix.