Invisible methods

R objects come with various methods that make them useful. I tend to stumble over these by googling something I want to do, and finding some code example on StackOverflow. But today I learned (from @RLangTip) that there is a straightforward way to list them all: you simply call e.g., methods(class='lm').

That's nice, but mileage varies and I don't have a good explanation for it. Take Zelig for example. It has this sim() function which produces a simulation object with some methods of its own. One of these is plot.ci(), illustrated here. Unfortunately, you won't find it with the methods() call:

> library("Zelig", lib.loc="C:/Program Files/R/library")
Loading required package: boot
Loading required package: MASS
Loading required package: sandwich
ZELIG (Versions 4.2-2, built: 2013-10-22)

+----------------------------------------------------------------+
|  Please refer to http://gking.harvard.edu/zelig for full       |
|  documentation or help.zelig() for help with commands and      |
|  models support by Zelig.                                      |
|                                                                |
|  Zelig project citations:                                      |
|    Kosuke Imai, Gary King, and Olivia Lau.  (2009).            |
|    ``Zelig: Everyone's Statistical Software,''                 |
|    http://gking.harvard.edu/zelig                              |
|   and                                                          |
|    Kosuke Imai, Gary King, and Olivia Lau. (2008).             |
|    ``Toward A Common Framework for Statistical Analysis        |
|    and Development,'' Journal of Computational and             |
|    Graphical Statistics, Vol. 17, No. 4 (December)             |
|    pp. 892-913.                                                |
|                                                                |
|   To cite individual Zelig models, please use the citation     |
|   format printed with each model run and in the documentation. |
+----------------------------------------------------------------+



Attaching package: ‘Zelig’

The following object is masked from ‘package:utils’:

    cite

> methods(class='sim')
[1] plot.sim*   print.sim*   repl.sim*   simulation.matrix.sim*
[5] summary.sim           

   Non-visible functions are asterisked

See that? There's a non-visible plot() method listed, but no plot.ci() method, yet it exists and it works. I wonder why that is. Is it maybe that plot.ci() is some kind of child of plot()? If so, how do you list such children?