Sometimes when you look at an approach chart, you see fixes that are labeled as IAF but have a gap between the arrow and the next fix (usually an IF).
For example, FIKDU on the KPRB RNAV RWY19 does not have a continuous arrow leading to the approach. However, it does have an altitude, direction, and distance so you can fly from FIKDU to MEETL.
It gets more complicated on the ILS Y RWY 16R approach. Notice that there are three arrows going from the Filmore VOR to the localizer. Only one of them is flyable. The other two are cross radials used to identify the JINAT and FURRY intersections. The R-235 radial from Van Nuys looks like it is a cross radial used to identify ZIDOM, but it is also flyable since there is an altitude, direction, and distance to ZIDOM labeled near the VOR.
If you are flying the LYNXX.EIGHT arrival it would take you to the VNY VORTAC. So how do you get to the approach if you are coming from the west at the Filmore VOR (FIM)? You fly the feeder route to ZIDOM—an IAF.