A newspaper puts three stories on its front page and finishes none of them there. On paper the eye manages: you read to the foot of a column, turn the sheet, and hunt for the heading again. On a screen that hunt is worse, because the column under the one you were reading belongs to a different story and looks exactly the same.
A PDF can say what belongs with what. Each story names the patches of page it is read through, in the order they are read, and reading software that follows one goes from the foot of a patch to the head of the next wherever it falls — the next page, the page after, the other side of the same sheet. The document below is a two-story newsletter, and the two swap sides between the pages on purpose: what you would read next by eye is not what you read next by following the story.
Nothing is left out and nothing is simplified: this is the program exactly as it runs, for the developer who uses this library. The third is the description itself: a plain list of what the page has to say, which is what the service is sent.
Read the Rust source Read the Python source Read the JSON source
A plain first slide and thirteen more, each stating the effect it arrives by — the twelve the PDF standard (ISO 32000) defines — how long that effect takes and how long the slide stands before the next one comes. The file asks to open full screen, which is where the effects play, and a link on the first slide shows the screen again, brought in by dissolving.
Four pages that say how they want to be opened: which page comes up and how much of the window it fills, the chapters beside it, the pages two at a time, a print dialog already filled in — every one of them a wish reading software answers for itself.
A document made to be followed rather than looked at: every line of the contents lands on the page it names, and every page leads back to where it came from.
Links and marks hung on text the engine has already placed: a band behind a line, an underline, a boxed cell — every rectangle taken from what the layout and the table report afterwards, none of it measured by hand.
Pages numbered by their labels rather than their position.
A half-price shelf card: every line shows the old price with a line through it beside the new one, the sum of the three carries a rule over the top, and the title is set a second time behind itself, shifted and paler, so it reads over anything.
