The document specifies both .iota and iota. as

In general, these procedures return the list whose elements are of the form
      FROM + i * STEP
where
      0 <= i < ceiling((TO-FROM)/STEP) (.IOTA)
      0 < i <= floor((TO-FROM)/STEP) (IOTA.)

While these may be a generalization of APL's iota,
what's the rationale for them, vs something like:

(iota count)            ; start=0, step=1
(iota count start)      ; step=1
(iota count start step)

?