The stack environment an AST node denotes directly: a .GlobalEnv/.BaseEnv symbol, a
globalenv()/baseenv()/emptyenv() call, the current env via environment(), the parent via parent.env(e),
or a named search-path entry via as.environment("package:x"). Returns undefined otherwise.
The stack environment an AST
nodedenotes directly: a.GlobalEnv/.BaseEnvsymbol, aglobalenv()/baseenv()/emptyenv()call, the current env viaenvironment(), the parent viaparent.env(e), or a named search-path entry viaas.environment("package:x"). Returnsundefinedotherwise.