alias_expr(alias) returns the expression that was used to define an alias.
alias_env(alias) returns the environment in which the aliased expression is evaluated.
alias_expr(alias, envir = parent.frame())alias_env(alias, envir = parent.frame())
alias_expr(alias) returns an unevaluated R expression (a name or a call).
alias_env(alias) returns an environment.
the name of an alias, as a string
the environment in which to look up the alias name (default: calling environment)