The strings a concatenation invents

The strings a concatenation invents

8 documents of 256 characters, run together. A window spanning a join is a string the collection contains; the upper line counts them and the lower counts the ones that occur in no document at all. At 12 characters there are 77 spanning windows of which 44 are new, and every one of them is a string an index over the concatenation will report and a reader looking for documents cannot use. Putting one separator between the documents makes the count of matchable artefacts zero at every length — a pattern drawn from a document cannot contain a character no document holds.

Drawn at 700 × 420, wide on the page. Everything above is what document-join returns with no arguments; the caption is the generator's own, computed from the numbers in the drawing rather than written beside it.

5 essays call document-join. The drawing above is what it returns with no arguments at all; every call below passes it something, because a placement that passes nothing draws whichever member of the family the generator happens to default to rather than the one its essay argues about — which is what optcheck and figfill exist to catch.