help_topic_target parses the expression being passed to the
help function call to find the innermost module subset expression in
it.
find_env acts similarly to find, except that it
looks in the current environment’s parents rather than in the global
environment search list, it returns only one hit (or zero), and it returns
the environment rather than a character string.
call_help invokes a help() call expression for a package help
topic, finding the first help function definition, ignoring the one
from this package.
help_topic_target(topic, caller)find_env(name, caller)
call_help(call, caller)
help_topic_target returns a list of two elements containing
the innermost module of the help call, as well as the name of the
object that’s the subject of the help call. For help(a$b$c$d),
it returns list(c, quote(d)).
the unevaluated expression passed to help.
the environment from which help was called.
the name to look for.
the patched help call expression.