apropos(what, where = FALSE, ignore.case = TRUE, mode = "any")
| what | the name of an object or a regular expression. what can be either a name or a character string; however, we recommend a character string for compatibility. | 
| where | a logical value. If TRUE, the names of the returned vector has the position of the package (in search()) that contains the object. The default is FALSE. | 
| ignore.case | a logical value. If TRUE (the default), uppercase and lowercase characters are considered equivalent when matching. | 
| mode | a character string. If it is not the default ("any"), only objects whose mode is mode are considered. | 
apropos("^x", ignore.case = TRUE, mode = "any", where = TRUE)
apropos("^x", ignore.case = TRUE, mode = "any")
apropos("^s", ignore.case = FALSE, mode = "list")
apropos(".data.frame$")  # Compare the result as: methods(class = "data.frame")