Task RDEPENDS vs. IMAGE_INSTALL

[Matt Darland]

I have a task with an RDEPENDS clause:

RDEPENDS_task-xxx-yyy = "\
  avahi-autoipd \
  tzdata-americas \
  some-other-stuff \
"

And an IMAGE_INSTALL:
IMAGE_INSTALL +=   "task-xxx-yyy"

When building the image, avahi-autoipd and tzdata-americas won't get 
installed, unless I explicitly add them to the IMAGE_INSTALL variable. Some 
packages work, and some won't (like the above example). What exactly are the 
semantics of RDEPENDS, and when something gets placed in the image?

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Thanks,
Matt Darland