annotations_in_spans(x, y)

## A simple text.
s <- String("  First sentence.  Second sentence.  ")
##           ****5****0****5****0****5****0****5**

## Basic sentence and word token annotation for the text.
a <- c(Annotation(1 : 2,
                  rep.int("sentence", 2L),
                  c( 3L, 20L),
                  c(17L, 35L)),
       Annotation(3 : 6,
                  rep.int("word", 4L),
                  c( 3L,  9L, 20L, 27L),
                  c( 7L, 16L, 25L, 34L)))

## Annotation for word tokens according to sentence:
annotations_in_spans(a[a$type == "word"], a[a$type == "sentence"])