Utilities for creating annotation objects.
next_id(id)
single_feature(value, tag)
an integer vector of annotation ids.
an R object.
a character string.
next_id() obtains the next “available” id based on the
given annotation ids (one more than the maximal non-missing id).
single_feature() creates a single feature from the given value
and tag (i.e., a named list with the value named by the tag).