Why is there a plot.lm help page while plot.lm function does not exist

I was trying to figure out which smoothed line was used in the leftover against the set default r plot

for an object lm

, so I checked the help page by typing ?plot.lm

, as my understanding <function>.<type>

is how these default behaviors are defined for different object types.

As expected, there was a help page, but it didn't specifically mention the smoothed line in the leftovers compared to the set schedule, so I wanted to test the underlying code, usually for a function that you can get by typing it into a console without brackets. but the plot.lm

console input gave an error object 'plot.lm' not found

. Since the man page talks about this in the package stats

, I also tried stats::plot.lm

it but had no effect. I tried plot

some plot.<something>

options like plot.default

, and they really existed and gave the code.

Why is there a help page for plot.lm

as long as there is no named function plot.lm

and where will the object's behavior be displayed lm

if not specified in plot.lm

?

I expect it has something to do with the difference between S3 and S4 methods, but I don't know enough about this R side to figure it out.