Text blocks should be constructed such that they 'honor and reveal' the relationships between the various elements - headings, subheadings, quotes, asides and footnotes. Robert Bringhurst recommends a character count per line of approximately 66 letters for optimum legibility, but accepts that anything between 45 and 75 is satisfactory.
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Duis nunc sapien,
venenatis ac tincidunt et, laoreet a augue. Cras condimentum enim at sodales tincidunt.
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Duis nunc sapien,
venenatis ac tincidunt et, laoreet a augue. Cras condimentum enim at sodales tincidunt.
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Duis nunc sapien,
venenatis ac tincidunt et, laoreet a augue. Cras condimentum enim at sodales tincidunt.
Lorem ipsum dolor sit amet, consectetur adipiscing elit. Duis nunc sapien,
venenatis ac tincidunt et, laoreet a augue. Cras condimentum enim at sodales tincidunt.