先听一个故事，我们经常遇到这样熟悉的味道

library(tidyverse)
── Attaching packages ─────────────────────────────────────────────────────────────────────────────────────────────────── tidyverse 1.2.1 ──
✔ ggplot2 3.1.0     ✔ purrr   0.3.0
✔ tibble  2.0.1     ✔ dplyr   0.7.8
✔ tidyr   0.8.2     ✔ stringr 1.4.0
✔ readr   1.3.1     ✔ forcats 0.4.0
── Conflicts ────────────────────────────────────────────────────────────────────────────────────────────────────── tidyverse_conflicts() ──
✖ dplyr::filter() masks stats::filter()
✖ dplyr::lag()    masks stats::lag()

suppressPackageStartupMessages 函数可以把所有的启动消息都隐藏起来

suppressPackageStartupMessages(library(tidyverse))

但是，我想说的不是这个，最近偶然看到，在 R Markdown 内还可以这样设置来屏蔽启动消息，是不是感觉很简洁很直观

```{r, echo=TRUE,R.options=list(tidyverse.quiet = TRUE)}
library(tidyverse)
```

这其实是 tidyverse 提供的一个选项

那么，我的问题来了，比如 knitr ，rmarkdown 等等其他的 R 包，如何比较方便地找出这样的隐藏选项呢？当然不单纯指隐藏启动消息这样的功能。

当然，我们也试过在启动了 R 包以后，这样找

names(options())
 [1] "add.smooth"                           "askpass"                             
 [3] "asksecret"                            "bitmapType"                          
 [5] "browser"                              "browserNLdisabled"                   
 [7] "buildtools.check"                     "buildtools.with"                     
 [9] "CBoundsCheck"                         "check.bounds"                        
[11] "citation.bibtex.max"                  "connectionObserver"                  
[13] "continue"                             "contrasts"                           
[15] "defaultPackages"                      "demo.ask"                            
[17] "deparse.cutoff"                       "device"                              
[19] "device.ask.default"                   "digits"                              
[21] "download.file.method"                 "dplyr.show_progress"                 
[23] "dvipscmd"                             "echo"                                
[25] "editor"                               "encoding"                            
[27] "error"                                "example.ask"                         
[29] "expressions"                          "ggvis.renderer"                      
[31] "help_type"                            "help.search.types"                   
[33] "help.try.all.packages"                "HTTPUserAgent"                       
[35] "httr_oauth_cache"                     "httr_oob_default"                    
[37] "install.packages.compile.from.source" "internet.info"                       
[39] "keep.source"                          "keep.source.pkgs"                    
[41] "locatorBell"                          "mailer"                              
[43] "matprod"                              "max.print"                           
[45] "menu.graphics"                        "na.action"                           
[47] "nwarnings"                            "OutDec"                              
[49] "page_viewer"                          "pager"                               
[51] "papersize"                            "PCRE_limit_recursion"                
[53] "PCRE_study"                           "PCRE_use_JIT"                        
[55] "pdfviewer"                            "pkgType"                             
[57] "plumber.swagger.url"                  "printcmd"                            
[59] "profvis.keep_output"                  "profvis.print"                       
[61] "profvis.prof_extension"               "profvis.prof_output"                 
[63] "prompt"                               "readr.show_progress"                 
[65] "repos"                                "restart"                             
[67] "reticulate.repl.hook"                 "reticulate.repl.initialize"          
[69] "reticulate.repl.teardown"             "rl_word_breaks"                      
[71] "rstudio.notebook.executing"           "scipen"                              
[73] "shiny.launch.browser"                 "shinygadgets.showdialog"             
[75] "show.coef.Pvalues"                    "show.error.messages"                 
[77] "show.signif.stars"                    "str"                                 
[79] "str.dendrogram.last"                  "stringsAsFactors"                    
[81] "terminal.manager"                     "texi2dvi"                            
[83] "timeout"                              "ts.eps"                              
[85] "ts.S.compat"                          "unzip"                               
[87] "useFancyQuotes"                       "verbose"                             
[89] "viewer"                               "warn"                                
[91] "warning.length"                       "width"

这种找法应该不全，剩下就是去翻 R 包的更新历史，主页介绍，最后是源代码？不知道有没有比较好的找法，捷径什么的，翻找的顺序什么的，有时候看到这样的 https://github.com/rstudio/bookdown/blob/master/inst/examples/index.Rmd#L24-L27
一半的选项不知道在干嘛，要从哪里找帮助说明