nl_tokens: String - > [ Element ] - > Element
pl_tokens: function flow ( direction , elements ) { var widths = elements . map ( widthOf ) var heights = elements . <mask> ( heightOf ) var width = direction === "left" ? sum ( widths ) : direction === "right" ? sum ( widths ) : maximum ( widths ) var height = direction === "down" ? sum ( heights ) : direction === "right" ? sum ( heights ) : maximum ( heights ) return new Element ( new FlowElement ( direction , elements ) , width , height ) }